Marine atomic tests cause changes in the ocean's ecosystem resulting in dangerous blobs of radiation and the resurrection of a dormant dinosaur which threatens London.
Gene Evans
as Steve Karnes
André Morell
as Prof. James Bickford
Leigh Madison
as Jean Trevethan
John Turner
as John
Alastair Hunter
as Dr. C. A. Morris, the village doctor
Lloyd Lamble
as Senior Admiral, at the Admiralty
Jack MacGowran
as Dr. Sampson, the paleontologist
Maurice Kaufmann
as Mini Submarine Officer
Henri Vidon
as Tom Trevethan
Patrick Jordan
as Photo Lab Aide
Howard Lang
as Naval Commader, at the "Valkyrie" wreck (uncredited)
Leonard Sachs
as Dialogue Scientist at Conference (bit)
