The Mohole Mystery is a juvenile science fiction novel, the eleventh in Hugh Walters' Chris Godfrey of U.N.E.X.A.

A drilling project in Dudley in the West Midlands region of the United Kingdom hits a cavern 20 miles beneath the surface of the Earth and detects strange microbes.

UNEXA send Russian Serge Smylov down to search for other forms of life in a rocket-propelled capsule but it is damaged when it hits the bottom of the cavern.

The book, under its US title The Mohole Menace, is mentioned in A Short History of Nearly Everything by Bill Bryson.

The project came to be called the "No Hole", and was discontinued by the US Congress in 1966 due to ever-rising costs and the fact that they had only managed to drill to a depth of 601 ft.[1]