 A serial killer known as "the avenger" is murdering blonde women in London. A new lodger, Jonathan Drew, arrives at Mr. and Mrs. Bounting s in Bloomsbury and rents a room. The man has some strange habits, he goes out during foggy nights and keeps a picture of a blonde girl in his bedroom. The Bounting s daughter, Daisy, is a blonde model and she is engaged to Joe, a detective. When Joe finds out that Bounting suspects Jonathan, he is jealous of the lodger flirting with Daisy and arrests the man accusing him of being the avenger.