The arrival of a new security officer – Haupman Ullman, leads to a tightening up of security. However the British contingent manages to eavesdrop on a meeting that will decide the strategic use of Colditz and they are surprised at what they learn. Meanwhile, the disillusioned German second in command (Michael Gough) is giving cause for concern with his behaviour, and when the Gestapo arrive, they spring a surprise on the Kommandant and his new security chief.