Dang it, this is why I try not to read a story that isn't finished. I wasn't going to, but the concept of Donnie Darko and Bobby Goren was just too freaking interesting to pass up. And now, I'm dying for you to continue and start posting more chapters to this! Please, soon, update? Just a few chapters here and there? Anyway, you write Donnie so well despite what you think. There were no bad chapters with this story, all were brilliant!
Frank does not melt. He's there one second, and then gone the next. There is also a type of barrier Donnie cannot go through. Possibly what separates the Primary and Tangent Universes.
If you want to make Frank disappear effectively, you must do it like in the movie: Distract Donnie. He'll listen to Frank, and when it's time for Frank to go, someone usually says something to Donnie, snapping him back to reality. That, or something else happens to distract him.
As you yourself stated, Frank doesn't say much. So it was good that you added that Donnie was confused by Frank's sudden interest in speaking. It confuses and entices the reader, as well as Donnie.
When Frank DOES speak, he usually is very evasive and unclear. He makes Donnie feel like he should already know the answers. Or he'll counter a question with a question. The best example of this is in the movie, when Donnie asks where Frank came from, he replies, "Do you believe in time travel?"
The best example of this in your story is (of course) when Frank asks, "Why do you ask so many questions you already know the answer to?"
Also, Frank doesn't move. If you watch the movie again, you'll find that whenever he speaks to Donnie, he's usually standing in some isolated corner. Please keep this in mind, as you've done very well with this compared to most other Darko fanfics I've read.
Now, a few things about Donnie:
He's very insecure. He doesn't like being questioned or confronted with new things, and responds to this rudely.
He's also, to some extent, very confident in his beliefs. He doesn't like being disagreed with, and hates ignorance. Best example of this in the movie is when he tells the teacher to shove the cards up her ass.
When he's acting on Frank's orders, he's not... himself. It's like he's in a trance of some sort. However, don't let this limit you. Donnie can still be active and whatnot, but just make sure he's not TOO active. You did a good job on this one with the scene where he confronts the psychiatric doctor.
Story-telling in general:
"He has to kill Donnie Darko..."
I really hate to be insulting, but it pains me to tell you how obvious this was. Especially with the loose ends and whatnot. However, you said you forced yourself to write this, so please keep in mind that readers hate stereotypes. This is why I said that although Donnie is usually in a trance-like state when acting on Frank's orders, don't make him too inactive. Try to avoid stereotypes in writing!
However, the chapter's been written, and as such the only advice I can offer you is either some accidental way or ingeniously clever way to avoid being poisoned.
So sorry for the long review, but as I stated before: It's an interesting story, and I'd hate to see such talent go to waste!
I begged you to update, and then it takes me this long to actually read it. Anyways, I love the chapter, and although I've only seen a few episodes of CI, I think your bobby is really nicely done.
That said, there is a few things needing explained.
I'm confused is this the same univers as when he was in mental hospital, and if it is, shouldn't the police know this and rule him out as a suspect?
Hope you update soon, cos this is getting better and better.
“I like this game. It’s universal, I can recognise it.”
Another good line.
Surprisingly enough, you make me regret that the story isn't finished. I usually read unfinished works and decide they're not worth reading, let alone reviewing, but yours has caught my attention.
I'm not much of a CSI fan, but I've seen a few shows and know how the characters act. It's interesting to see Donnie match wits with them.
Of course, you'll have to include that oh-so-clever way of finding the real killer and still develope Donnie's character. I suspect that will be somewhat of a challenge.
Good luck to you on that, I'll keep an eye out for the next chapter!