Terence Fisher directs this sci-fi horror starring Christopher Lee and Peter Cushing. When a freak heatwave in the middle of winter sends the temperature soaring on the remote island of Fara, the locals, including Dr Vernon Stone (Cushing) and novelist Jeffrey Callum (Patrick Allen), are left dazed by the rising temperature. When Callum is reunited with his former mistress Angela Roberts (Jane Merrow), the atmosphere becomes even more tense. It is left to Godfrey Hanson (Lee), a visitor to the island, to solve the mystery of the deadly soaring temperatures.