In 1940, after the fall of France, the fictitious Channel Island of Armorel is occupied by a small garrison of German troops under the benign command of Hauptmann Weiss.

Back in London, the Ministry of Agriculture realise that during the evacuation of the island, Venus, a prize pedigree pregnant cow, was left behind.

They petition the War Office to do something urgently due to the value of the cow's bloodline, and Major Morland is assigned the task of rescuing Venus.

They, radio operator Sergeant Forbes and naval officer "Trawler" Langley, who knows the local waters, are taken to the island by submarine.

They spirit the cow and her calf onto a Royal Navy Motor Torpedo Boat which takes them to Britain, sinking a pursuing German E-boat in the process.

He said this "was a sod because we shot mainly on location, and every time it rained, which it did regularly, the colours would run, and you would think the cow was milking itself because drops of paint were falling on the grass.