In the Bleak Midwinter - Kit Hardwicke, #1

Take four men, a green dog, an impossible espionage task, mix together and drop into an alternative World War I snowstorm. The narrator has to juggle three different identities and has to keep track of which of his alter egos speak which languages. They all ought to be killed at any moment, and any other moment, but they still occasionally find time to feast. There are bats everywhere in midwinter.
They are following  wild goose chase, but there are no geese. Is the narrator succumbing to PTSD? Is his best friend, his very very best friend, being drugged by the strange woman in Constantinople? What is the blood thirsty German General injecting himself with? Is anyone who they seem? A bit steampunk, with extra bats.