Actually, what he says is "I’m going to church with you." But Waterhouse, the cryptologist, is engaging in a bit of secret code work here. He is using a newly invented code, which only he knows. It will be very dangerous if the code is ever broken, but this is impossible since there is only one copy, and it’s in Waterhouse’s head. Turing might be smart enough to break the code anyway, but he’s in England, and he’s on Waterhouse’s side, so he’d never tell