Hmm, an interesting one. I always want to reward films that make an audacious decision midway through but I can't help feeling like this is a better film before it lays its cards on the table. But I found the later stuff quite charming even if I wasn't fully able to follow it on the weird little diversion it takes along the journey.
All the early in-car stuff is wonderfully tense and Rosamund Pike and Matthew Rhys do a great job as the only real onscreen presences - not sure I'm quite as convinced with the elements of their performance that fall outside of that...