The objective of the exercise is to transport a highly important agent (Mainwaring) to a selected destination while avoiding the best efforts of counter-agents GHQ has put out to capture him.
Making surprisingly good progress, they also manage to avoid the schemes of Hodges and the Verger who, while walking through some woodland, are suddenly pursued by what appears to be a gorilla.
Sensing a ploy, the men dismiss this information, even when Hodges, having taken refuge in a tree, tells them of the animal he and the Verger encountered.
After the men go to sleep, the gorilla sneaks away and returns to GHQ, where it is revealed to be an officer, Lieutenant Wood in disguise, spying on the platoon.
Pressed for time after Mainwaring's inept skills with a compass get them nowhere, he and Jones commandeer Hodges' motorbike, with the rest of the platoon following in the van.