A disgraced school master, Benjamin Twist, is mistaken for a tough prison governor and assigned the charge of a prison for particularly hardened criminals. Believing he is being sent to a school rather than a prison, he celebrates accordingly only to find that his drunkenness accidently lands him on the wrong side of the prison bars. The Governorship is eventually restored to him, and he sets about popularising himself amongst the convicts by turning a blind eye to their shady dealings.

Through the influence of a relative, a hopeless railway employee is made stationmaster the sleepy Irish station of Buggleskelly. Determined to make his mark, he devises a number of schemes to put Buggleskelly on the railway map, but instead falls foul of a gang of gun runners.

Will Hay plays a bragging sea captain whose maritime experience actually extends to navigating a coal barge down inland waterways. His tall tales catch him out when he is co-erced into commanding an unseaworthy ship by an unscrupulous shipping agent who means to have it wrecked. This was the first film to couple Will Hay with both Moore Marriott and Graham Moffatt.

Nazi spies are out to destroy a new submarine killer, the "Firefly", being developed by the British navy. A hapless waiter named George, after being rejected for military service three times, finally "joins" when, during an air raid, he is mistaken for a real sailor. He soon unwittingly stumbles into the secret hideout of the Nazi spies trying to destroy the Firefly. Complications ensue.