A freak heat wave sends the temperatures soaring on a remote island. Dr Stone (Peter Cushing) and Callum (Patrick Allen) try to uncover the mysterious reason for the sudden change in climate. But the arrival of Callum's former mistress (Jane Merrow) forces the atmosphere to boiling point and it falls to Godfrey Hanson (Christopher Lee) to discover that the rising heat is the start of an invasion of merciless aliens..
