Zig-Zag was the codename of Eddie Chapman, a criminal imprisoned in Jersey for safe-breaking[?] in Glasgow. On the occupation of the Channel Islands, the Germans recruited him as an agent and despatched him to mainland Britain to commit acts of sabotage. He was turned and was used to feed misinformation to the Germans.
... but, later that evening, Kitty rejects him in the expectation that Vronsky is about to propose to her.
The following morning Stiva and Vronsky are at the station to ...