Even with a little help from some people in the audience, I'm not sure I can say that Trance makes complete sense.
I'm not even sure I can give you suggestions that might help you follow th eplot better than I seem to have, though I will suggest that you keep a close eye out for exactly when James McAvoy gets hit by the red car-- the timing seems to be extremely important as to the question of how the original theft of the painting was planned and actually took place.
Even my advisers admitted that things got pretty cloudy after that.
Vincent Cassel bashes McAvoy in the head, which is the big mistake that fouls everything up, because it gives him amnesia and he can't remember where he hid the loot... if he hid it at all, which I think he did, because Cassel's treatment for amnesia is not such as many people would endure if they could help it. And I don't think McAvoy is faking, although in terms of such credibility as is required by the plot of Trance, he could be.
Anyway, the gang calls in Rosario Dawson, who must be the most awesome hypnotist of all time, to revive McAvoy's memory, and from then on we get a mishmash of memory and imagination and historical fact and induced ideas and just plain beautiful photography as we are surely not expected to make complete sense of, certainly not on a first try.
And then there's a veritable vomiting of violence at the end that Quentin Tarantino would be satisfied with.
A retrospective narration by one of the characters at the end clarifies things enough that I was tempted to go back and try another look at Trance, except that I resent these unintelligible puzzles that are fashionable today.
If I want to be bewildered, I'll buy me a Rubik's Cube.