More soap opera than true crime, but this cinema advert is almost as cunning as its onscreen detective.

The mystery of the bogus brother burglar - a case for Sherlock Foams? Like many of the best cinema ads from this period, the puzzle for audiences was how the carefully crafted story was going to twist into a sales message. The reveal here is distinctly clever, as the clue that cracks the case highlights the USP of the product. Elementary, my dear Persil.

Advertising film for Persil washing powder.

A man climbs through the window into a darkened house, and is startled when
the lights come on and a police inspector, who recognises him as a thief and
saw him enter, confronts him. The man claims that it is his sister's house
and he lives here, but forgot his key. To prove his case he describes the
layout of the house in detail and the inspector checks, having first hand-
cuffed the man to a chair. The man asks to be set free, but the inspector
still doesn't believe his story. He has noticed that all the sheets and
tablecloths in the house are gleaming white, whilst the man's shirt is dull.
If he lived in the house his shirt would be the same, the clue came when he
spotted a box of Persil in the kitchen.