Despite my misgiving at doing another crossover, I felt like a Dresden Files/Felix Castor crossover was kind of obvious. And this particular prompt inspired me to go there, given Felix's methods. For those who haven't read the Felix Castor novels, you won't be confused reading this story. All you need to know is that Felix is a British exorcist living in London. The rest is explained in the fic.

Every profession's got an unsolvable puzzle.

The evolutionists have the Missing Link.

The historians have Stonehenge.

And for awhile the mathematicians had Fermat's Last Theorem before that Wiles bloke came along and solved it. So never mind that example.

My point is, a lot of professions have that one case, that one element that always remains unsolvable and soon, moves into legend. For us exorcists, we have Hrothbert of Bainbridge.

I was still a student at Uni when I'd first heard of him, the ghost who could never be exorcised. A professor of mine said he'd met the spirit once, even feeling the curse that bound the ghost to his own bones, unable to move on, unable to rest. Tied to this world, not by choice like most spirits, but forced. Apparently, he had been some sort of sorcerer who had done some terrible things in his life. But it had been one particularly horrible act that had earned him a curse that made it impossible for any of us to banish him to the next beyond.

There were people in my field who often talked about being the one to finally release the Bainbridge ghost. Years after leaving school and starting to make my way, I'd met colleagues who claimed to have encountered the infamous specter. Of course, no one had managed to exorcise him, though. Stories sprung up and grew as the skull that trapped the ghost moved around the world and into the hands of various owners. I never really put much thought into tracking it down myself. My job was to get rid of ghosts, not dwell on ones that were proven impossible to shift.

And then times changed, the once booming business dried up and I was in need of a job. Looking back on it, I see it was a little thick of me to agree to a case with only vague outlines and slim details that made it sound too good to be true. Hadn't I learned by then that things too good to be true were exactly that? Regardless, Pen had put in me touch with these people who were in need of an exorcist. And I owed Pen the money they were offering to pay for months of backed up rent and it seemed a little too awkward to turn them down. So a phone call later, I was paid my full fee in advance and on a plane for the first time to America. First class, mind you.

Ten hours later I was in the half abandoned wine cellar of some rich ponce's house in Chicago, staring at a cage that held a very old, very famous skull.

See? Too good to be true.

You might wonder what I'm grousing about. What I basically described was that I was given an all expenses paid trip, plus my fee to try and exorcise a spirit that legend told was impossible. If I was successful, my fame would spread throughout my little occult world. If I failed then hey, better exorcists before me had been defeated. So where was the harm, you might ask.

Well, I'll tell you: I don't like messing with cursed things. I have enough of my own troubles and handling something with a hex on it wasn't going to help matters. And this was exactly what I told my two new clients upon being faced with the task at hand.

"You agreed to our case, Mr. Castor," said Client #1, looking put out.

"You said you needed an exorcist to get rid of a ghost. You didn't say anything about the ghost being bloody Hrothbert of Bainbridge!" I retorted. "It can't be done."

"You came to us highly recommended. We hear you are the best," stated Client #2, who was apparently taking on the role of good cop.

I'd like to think my skills had garnered me the reputation as being the best, but chances were I was simply the next exorcist on a very long list. Most likely nearer toward the bottom. So to be more specific, I was probably the next best one who hadn't yet failed. "We only ask that you try," #2 urged, his voice silkily diplomatic and encouraging. I think I liked #1 more. He currently hated me but at least he was straight forward in his loathing.

I suppose I could have continued to refuse. But it dawned on me that there were two of them, one of me and they were blocking my exit. So here I was, in a basement in Chicago of all places left with the task of vanquishing the most famous ghost of my profession. I might add that the two people who hired me chose to leave me down here alone rather than hang about and see me in action. It's not an important detail, but I want to paint a very clear picture of the kind of cowardice I was working for.

Being in a darkened room, surrounded by old wine bottles and cobwebs, I wasn't exactly sure what to expect when a trail of smoke and yellow sparks leaked out of the skull and took form next to it. And then there he was. So maybe I hadn't been sure what to expect, but I wasn't thinking it'd be a neatly dressed gentleman in an ascot. He glanced around the room with more irritation than anger before resting his pale eyes on me.

"You must be the exorcist," he said. Nothing quite like a ghost looking bored at my profession. Does wonders for the confidence.

"Felix Castor," I introduced myself.

The ghost gave me a little nod. "Pleasure." There was an awkwardly long pause as I tried to figure out what to do next. "I suppose you must attempt to banish my soul," the spirit finally said, as if giving me cues. This was off to a great start.

"It's nothing personal," I explained, reaching into my coat pocket. "It's a job."

"By all means."

I felt the warm metal of my whistle inside the pocket, but only fingered the instrument. Was I really going to do this? I'd never been squeamish about banishing a ghost before, but this was no ordinary ghost. Even making the attempt at this exorcism felt too arrogant for my tastes. And the patronizing look the pale figure was giving me at my hesitation wasn't helping matters. With a little more determination, I pulled out my whistle and put it to my lips.

Every exorcist has their own way of getting rid of a ghost. But the commonality in all of us was that we had to find a way to capture their essence and bind them in order to banish them. Exactly how we trapped their souls was up to whatever felt most natural to us. Many used spoken words, some drew pictures. I'd even met a woman once who slapped down playing cards in some sequence only she could decipher to capture a spirit. I used music. Specifically, I played notes on my whistle until eventually, I'd come up with a song especially fit for the spirit in question. Once that was established, I'd play the tune to its completion and upon the conclusion, the spirit would be sent on its way.

I'll admit I was burning with curiosity as to what Hrothbert of Bainbridge's song would sound like. I started out with my usual opener of a scale and soon began to pick out certain tunes, notes, trills. During the entire process, the ghost wandered around the cellar, reading the labels of the various wines left over, looking unconcerned. Finally, after almost 20 minutes of experimenting, I finally settled on a noticeable melody and went with it.

It was an strange little song. Simultaneously melancholy and sparkling. Powerful, but restrained. On top of that, there was an odd discord to the tune that try as I might, I couldn't shake off. I felt a small shiver of anticipation when I saw the ghost looking at me finally with a quizzical expression. This might actually be it. I might actually exorcise Hrothbert of Bainbridge's ghost.

But my shocked victory was short lived as I felt the tune change and the dissonance I'd heard earlier only got more pronounced. The essence I'd felt in my hands slipped out from under me. I tried again to capture it, but it only continued to skitter away. I kept chasing after it, but it was like trying to stab an especially hard pea with a dull fork. After a half hour, I had to take a break.

"I don't think I've ever met an exorcist who used music before," commented the ghost, staring at my whistle.

That was a surprise. "Really? Aren't you over 800 years old? I would think you've seen everything."

"You might be shocked to learn, Mr. Castor, but existing for centuries does not necessarily mean I get to enjoy my immediate surroundings," he replied, coldly. Okay, so that had struck a nerve. For a spirit that people wrote nightmares around, he was a bit sensitive.

I went back to concentrating on the tune I'd been more or less forced to abandon. It was pretty obvious that there was some sort of protection field around the skull itself, keeping it from damage. But that shouldn't have stopped me from picking out the spirit's tune. It was more like I couldn't get a proper grip on his essence because something or someone was already wrapped around it, keeping it away from the touch of others. I considered the odd discord in the melody I'd heard earlier.

"This tune of yours," I said, waving my whistle a little for emphasis. "It's a strange one. It's like you've got two different songs in you. One on top of the other."

"You can dissect it however you like, Mr. Castor. I doubt you'll be successful in your attempt tonight."

"You sound pretty confident."

He gave me an exaggerated smile. "As you know, this is the not the first time someone has attempted to banish me."

"Any idea why my clients want you gone?" I asked. I was a little curious about that myself.

The ghost heaved a sigh. "In this case I'm afraid it has less to do with my own transgressions and more of an attempt to cripple my current owner." He looked over at me and saw the confusion I was broadcasting. "Harry doesn't have very many allies," he added in a gentler tone as if that explained anything.

"This Harry bloke owns you?"

"He is the current keeper of my skull. And by that right, he is the one I serve."

My mind rifled through all the legends I'd heard of Hrothbert of Bainbridge. And the final psychological profile I came up with told me he wasn't someone who'd be well pleased to be someone else's servant. "I'd imagine you'd rather be gone than here," I guessed. Not giving him a chance to answer, I launched into his tune again. It went on a little longer this time and I could feel my metaphorical rope snake around his being once again….only to have it slip away as a dissonant note shrieked out from my whistle.

"Bollocks," I cursed. When I glared up at the ghost, he was giving me a mild "I told you so" look. "This song isn't completely yours," I said, almost accusatory. "Something else is mixed in with your soul or something." Judging by his expression, this was news to him. I wondered if whoever or whatever had cursed him to this existence had done it in a manner that not even he was aware of. "You don't look all that disappointed that I can't shift you to the next level."

He shrugged. "Many have tried before you. I'm sure many will try after you."

"Not exactly my question, is it?"

"You didn't ask a question."

"From what I've heard about you, I didn't mark you for the type to enjoy being a servant for another person," I said, crossly. Maybe I was being petty now. I'd just gone through thinking it was arrogant to even try exorcising this particular ghost and here I was sitting with wounded pride that I couldn't do it. "Wouldn't you rather one of us succeed?"

The spirit wandered over to the only small window in the cellar, staring out into moonlit grass outside. "Life with Harry has proven itself to be unconventional. And quite different from anything else." He just stopped again, as if he'd explained enough.

"Did you really bring someone back to life?" I couldn't help asking.

He turned to stare at me as if he'd just noticed I was in the room. After a moment's pause, that smile showed up again. "Have you ever done anything you've horribly regretted, Mr. Castor?"

For a second I wondered if by some magic, he had been able to look into my head and see my memories, my past and the guilt that weighed inside. I quickly brushed the thought away as paranoia, but still answered with a truthful, "Yes."

"Then you must know how it feels to wish to continue existing so that you might one day ease your guilt by becoming a better man."

"We're talking about the living." So that was insulting. Even I gave myself a mental slap across the head for it. But he strangely didn't look that bothered.

"Conventional lines tend to blur when I am with Harry," he replied instead.

I was working up to a response to that when I heard a loud crash above me. Pounding footsteps and breaking furniture brought down small clouds of dust from the ceiling on to my head. "Ah," said the ghost. "The Cavalry has arrived."

Rising up from my seat, I moved up to the steps leading to the first floor as the sounds of destruction continued. I lifted the cellar floor board about an inch or two off the ground and peered through to get an idea of what was happening. Client #1 was lying about three feet away from me, looking dazed rather than dead. His companion was currently in the middle of defending himself against a tall man wielding a hockey stick with a startling amount of determined fury. The choice of weaponry had me lifting an incredulous eyebrow until I saw a bolt of blue light streak out of its end, catching Client #2 square in the chest, blasting him across the room.

I quickly replaced the floor board and retreated back down the stairs.

"I'll hazard a guess the man with the hockey stick is your owner?"

"Yes, that would be him." The ghost gestured toward the cellar window he'd been staring out of earlier. "I'd suggest you make your escape through here, Mr. Castor." I gaped at the assistance, which didn't go unnoticed. "I have no quarrel with you. As you say, you were only doing your job and from what I've heard, with less enthusiasm than most. But when Harry gets in this mood he's likely to shoot you first and ask questions afterwards. I would go," he advised.

The one benefit to being close to penniless is that it leaves you nice and thin. I was able to slide out of the snug window with some effort. My feet barely cleared the frame before I heard the cellar door being wrenched open.

"Bob! Bob, you down there?" a voice shouted.

"Yes, about time."

I rolled over and leaned against the house, next to the window, under a bush. From this vantage point, I could see a Jeep parked out in the driveway.

"Where's the ghostbuster they hired?"

"Escaped a little while ago," answered the ghost, his voice a contrasting calm against the bubbling anger I could hear in the new arrival's tone. "I wouldn't worry about it too much."

"The hell are you talking about?! They tried to kill you!"

"I'm a ghost, Harry. They can't kill me."

"You know what I mean."

"Yes, I do. And thank you. But you've dealt with the men who originally stole my skull."

"They're just knocked out."

"The exorcist they hired was merely brought in as a third party," the ghost continued. "I don't believe he himself has any desire to relieve me of this world."

I got the feeling he was telling that to me, rather than just saying it. Either way, I wholeheartedly agreed. I stayed where I was, which was murdering my backside, as the skull's owner retrieved his lost property.

"When we get back, those protection wards are going back up," I heard him say. "Those defensive sigils did crap against those guys."

"Perhaps because they were invited in," the ghost mentioned.

"I know, I know. That was dumb. I'm sorry."

"No harm done."

"Your skull stays in the lab. At least for this week. I gotta talk to Morgan. There has to be a better way of keeping you out of trouble."

"One lives in hope."

The sarcasm reigned high in their conversation, but underneath it, I could hear the other aspect of their words, the things left covered, unspoken. I wasn't exactly sure what to even make of the shortened name. The bush I was half hiding under shielded me from being spotted as the man named Harry got into his Jeep, his hockey stick in one hand and the skull in the other. I watched him drive away before getting to my feet.

I gave the house a speculative glance, wondering if I should go in to see how my former clients were doing. But I decided against it, realizing I'd probably be left with borrowing their car to get back to the airport. So my first trip to the States and I'd added myself on to the list of people who'd failed to vanquish the ghost of Hrothbert of Bainbridge. And I got the feeling that true to the legend, the ghost wasn't ever going to be exorcised.

At least not until he was ready.