Context: Germans captured Carnaby while he traveling to Russia. Kramer and Rosemeyer are trying to get information from him. Germans captured some rescuers (British Agents) who are trying to save Carnaby from them. Kramer gave a drink to Carnaby but Carnaby not consuming it, so he said this words to Carnaby.
You are not drinking, general. That's understandable when your rescuers turn out to be, well, birds of a different feather.
Does it means Rescuers are Germans but disguised as British agents?