When a government official disappears in the London tunnels, after several reports of missing people in the same location, Scotland Yard start to take the matter seriously, along with a couple who stumble into a victim by accident.

Donald Pleasence
as Inspector Calhoun

Norman Rossington
as Det.Sgt. Rogers

David Ladd
as Alex Campbell

Sharon Gurney
as Patricia Wilson

Hugh Armstrong
as The "Man"

June Turner
as The "Woman"

Clive Swift
as Inspector Richardson

James Cossins
as James Manfred O.BE.

Heather Stoney
as P.C.W. Alice Marshall

Hugh Dickson
as Dr. Bacon