Based on the true story of the Portland Spy Ring. Bernard Lee takes time off as M to play hard drinking loose cannon Harry Houghton. Sacked as an embassy attaché in Warsaw. He bids a drunken farewell to his girlfriend who works for the Russians.

Harry is posted at a secret a Royal Navy equipment testing facility at Portland. He is soon approached by secret Soviet intelligence to hand over documents to them with the veiled threat of blackmail. After all he used to drunkenly tell secrets to his girlfriend back in Warsaw.

Harry realises that to take the documents from the safe. He needs to seduce work colleague Elizabeth Gee as she has the keys. She nervously and reluctantly agrees.

Once they get used to the money paid by his handler Gordon Lonsdale (William Sylvester.) They enjoy the good life, not realising that they have attracted the attention of the authorities suspicious of traitors in their midst.

Lee plays Harry as a bluff chancer. A cynical drunk and not too bright. Margaret Tyzack makes more of an impression as Gee, seduced by the good life and greed.

The movie has a documentary setting but plays it too safe and straight.