The place is London and the city is being terrorised by a serial killer known as 'The Avenger' whose victims are all blonde women. On a bleak day a stranger arrives at the door of Mr and Mrs Bunting enquiring whether they have a room for rent. Despite the events taking place in the city they decide to take him in. It isn't long before their new lodger, Jonathan Drew (Ivor Novello) takes a fancy to their daughter Daisy who happens to be a blonde model. But his flirting has been noticed by Daisy's boyfriend Joe Chandler who also happens to be the detective on the Avenger case. To Joe Mr Drew's behavior doesn't seem to add up...he only goes out at night and has a picture of a blond girl in his room. Drew's closeness to Daisy and his mysterious comings and goings are enough for Joe to act and name his as a suspect but is Joe's jealousy and Jonathan's odd behavior enough to prove a man guilty of murder?