Fun little elimination based logic puzzle, good for a casual round or two, and very well presented in terms of graphics, sound, and the overall conceit.
Quick QA note:
Am I right in thinking that the game generates the conditions for who's to be the spy randomly? At one point, I got a range of times for when they could have got on that was much larger than the range of times are which they got off, which worked logically but didn't feel entirely natural.