Blackwood grabbed the armrest as the SUV swung through the entrance ramp at a fairly high rate of speed. He let go once they were moving straight again. Ironhorse was driving, which was not a particularly relaxing experience - but Blackwood wanted to sit in the back with the fairly traumatized scientist and make sure she did not move from mild shock to anywhere worse. He touched her shoulder, and she turned to him, her eyes wild.

"They're back," she said, quietly.

"Not exactly." Blackwood took one of her hands in his. It shook. "These are the same aliens that the bacteria defeated in 1953. But they became contaminated with radioactivity, which killed the bacteria. They've been revived."

"They can take human form, now." She shook her head in disbelief. "How can they do that?"

"It's not exactly taking human form," Blackwood replied. "They take over human bodies. There's some type of cellular fusion that occurs. One of our scientists is trying to characterize it."

"That's fantastic. And not in the 'marvelous' sense of the word." Her frown deepened. "The chances of them sharing any kind of signaling molecules with us - let alone genetic material - are just about nil. You'd have a better chance of reproducing with an ear of corn!"

"I know it seems impossible, but somehow, they do. You saw it. We have very little information so far. The taken-over bodies dissolve almost immediately when they die, so we have had little chance to study the process."

Glastonye leaned back, rubbing her chin. She seemed calmer when she was approaching the reality of Aliens Among Us as a scientific problem, Blackwood noted. He sympathized entirely. "They could do it if they shared some very basic molecules. Maybe they're a small-molecule-based lifeform. Second messengers as their only components. That would also explain why they can stand radioactivity that's high enough to kill the bacteria. No genetic material to break down." She pondered further. "Perhaps their native planet is high in gamma radiation."

Blackwood pondered that. It was a very tidy hypothesis, actually. "You should speak with our molecular biologist, Dr. McCullough. She'd have some thoughts on that, I'm sure, but it's an intriguing idea."

Glastonye barked an unamused laugh. "I'm no molecular biologist, my boy. I took the small amount that was requisite to do my neurology. We should stop by Berkeley. I have a colleague at the University there. A young man who doesn't mind the comments of an old kook as long as they're to the point. He works on cell signaling."

"That sounds..." Blackwood grabbed the armrest again as the SUV abruptly decelerated and skewed to the side. "The hell?" he barked up front as they came to a stop.

"Five minutes." Ironhorse pulled something out from under the passenger's front seat and exited.

"Just a moment," Blackwood told Glastonye, and stepped out. He ran around to the back, where Ironhorse was swiftly swapping the license plate with one he had pulled out from under the seat. "What is this?"

"One of those aliens was a State Patrolman," Ironhorse told the new plate as he screwed it in. "He might have sent our plate around."

"How long have you been this paranoid, Paul?"

Ironhorse looked up at him, his eyes narrowing. His voice dropped half an octave as he purred, "And just why are you asking that?"

Blackwood did laugh, and felt a certain amount of tension ebb out of him as he did. He hadn't realized how much he had built up over the afternoon. He sighed. "We're stopping at UC Berkeley on the way back."

"Why?" Ironhorse walked to the front of the vehicle to finish the plate swap. Blackwood followed.

"Glastonye has a colleague there who is into cell signaling. I want to talk over an idea she had."

"That's a negative." Ironhorse finished screwing in the plate, stood, and looked Blackwood in the eyes. "We've been attacked once on this trip already. We're going to get you and the doctor to safety. You and McCullough can go see this fellow later, when we have time to plan a proper trip."

"It's on the way back."

"It'll be on the way out, when we do go." Ironhorse turned and re-entered the vehicle, tossing the old plates on the passenger's seat and buckling himself in.

"It'll be a quick stop." Blackwood leaned on the door.

"It won't be a stop at all."

Blackwood, tired of arguing, barreled on as if the man hadn't said anything. "We wouldn't do it if we weren't so sure you would take care of anything that came up." He hopped into the back. "Drive on, Jeeves!"

Ironhorse grunted.

------

It was somewhere between late night and early morning when they arrived back in the Bay Area, but Glastonye directed them to campus, rather than to a private residence. "He has a lovely house in the hills, but he's working on a grant. He won't sleep until it's done."

She called up from a public phone, and they waited at the door to one of the looming, dark buildings. A small dark-skinned man poked his head out of the door after a few minutes. His hair was disheveled and his eyes red-rimmed. "This is a surprise!" he said in a gravelly voice.

"Sorry to drop by with so little notice," Glastonye responded, "but these fellows wanted to talk to you about signaling."

"It couldn't have waited until morning?" the little man groused. But he stepped back, leaving the door open. The trio of visitors walked in after him, then followed as he lead them to an elevator. He introduced himself to Ironhorse and Blackwood as Dr. Pratech, and nodded curtly instead of shaking their hands.

He lead them to a small lounge on an upper floor. The three men sat; Glastonye begged a moment to visit the women's room.

"What is all of this about?" Pratech asked, yawning. "And why did my esteemed colleague bring you here at such a godforsaken hour?"

"Well, it's a bit complicated." Blackwood noted that there was a small coffee maker in the corner, and walked over to start a pot. He was used to going long stretches without sleep when it was necessary, but he never said no to a little assistance. "We have... a paradigm of cell fusion. We've no experience in it, and could use a little input."

"Tell me more," Pratech responded.

Blackwood tore open a single-pot pouch of coffee and dropped it into the basket. "The fusion involves a cell type that might well have no genetic material of its own."

Pratech snorted. "What kind of a doctor are you? Every cell type has genetic material. Even viruses do."

"This doesn't." Blackwood poured water into the coffee maker and started the brew, then turned to face Pratech, putting his hands on the counter behind him. "It's something previously uncharacterized."

Pratech's teeth flashed a startling white in his dark face as he grinned. "Well, this might be amusing. Go ahead, tell me more about this wonder-cell of yours."

Blackwood started to speak, then paused as Glastonye walked in. Something struck him as very strange about her; her walk was too stiff, and she looked straight ahead. Before he could digest those data, she raised her right hand, which had a revolver in it, and fired two shots. Pratech slumped over the table. Ironhorse leapt to his feet, pulling his own gun out and readying it - but he paused, and then fell as Glastonye fired twice more.

Blackwood snapped out of his shocked stillness. He grabbed the coffeepot and slung scalding-hot coffee at Glastonye. The shriek she let out as it splashed over her head was guttural and inhuman; she dropped her gun and clawed at her face.

A fire extinguisher stood in the corner, and Blackwood picked it up. He paused for a moment, looking at the frantically wailing Glastonye. He was a pacifist, he raged internally. Just because what he was about to do did not involve a gun did not make it any less an act of murder. Murder of a colleague, of a scientist - no, of an alien, an alien who had shot his friend. He swung the fire extinguisher, and it connected with a sickening crunch. Glastonye fell to the ground, her head crushed and oozing green blood.

Blackwood ran to the table. Pratech had been shot twice in the chest; Blackwood could feel no pulse in his neck. Ironhorse was twitching, however. Blackwood knelt by him. Glastonye must have had more trouble with a moving target, he thought with some relief; bloodstains were spreading rapidly from Ironhorse's shoulder and side, but he was still alive and conscious. "Just lie still," Blackwood muttered, pushing Ironhorse back down as the man tried to sit up.

"I couldn't do it," Ironhorse growled through his teeth.

Blackwood tore a strip from the man's shirt and tied it tightly around the wound in his shoulder. He wadded up his own shirt and pressed it tightly to the hole in the other man's side. "You liked her, and so you hesitated. That's a good thing, Paul. It means you're human."

"Don't patronize me. Help me up. There might be more of them out there."

"I'll take a peek. You stay here." He put the hand from Ironhorse's uninjured side on his makeshift compression bandage, then skulked out into the hallway.

In the lurid green glow of the Exit sign lighting, a security guard's uniform lay on the floor in a steaming puddle of goop. Blackwood stepped over it, looking for a telephone. He would have to get Paul some help, and also call in to the cottage. He could tell them that a major mystery surrounding the invasion was now solved.

A pity that the answers to mysteries are not always satisfying, he thought.