Night of the Big Heat

The heatwave is caused by the extraterrestrial beings inhabiting Fara. These aliens generate extreme heat as a byproduct of their presence, raising temperatures into the nineties during what should be a bitter British winter. The unnatural heat disrupts normal island life, cars stall, bottles shatter, and communications fail.

The oppressive heat begins immediately after Godfrey Hanson arrives, hinting at his connection to the alien presence.

The aliens are heat-based extraterrestrial beings that have invaded Fara island. They emit extreme heat that burns anything approaching too closely. They are invisible or at least unseen by most characters, appearing only through their effects, burned bodies, scorched sheep, and the mysterious high-pitched whirring sound that killed the tramp.

Hanson's secretive behavior with motion cameras and soil samples suggests he already knows about the extraterrestrial threat before anyone else.

The aliens are drawn to light sources, which becomes evident when Stella Hayward is killed during an attack linked to her exposure to light. This attraction is later exploited when the group uses flare pistols as part of their defense plan. The aliens' gravitational pull toward light makes them dangerous to anyone using torches, car headlights, or other illumination on the island.

Bob Hayward's earlier attack occurred when he was driving with headlights on, foreshadowing the light-attraction pattern.

The aliens are vulnerable to water, specifically rain. When a sudden thunderstorm breaks over Fara, the downpour proves fatal to the extraterrestrial beings. The moisture or temperature change from the rain destroys them, ending the invasion. This turns out to be the aliens' critical weakness, the same extreme heat that makes them deadly to humans makes them susceptible to water and cold.

The extreme heat generated by the aliens creates the conditions for a dramatic weather reversal, setting up the storm's arrival.

Tinker Mason, already psychologically unraveling from the oppressive heat, attacks Angela Roberts in the pub. The exact motivation is unclear, possibly driven by heat-induced madness, jealousy, or general hostility. Angela defends herself by striking him with a heavy ashtray, knocking him unconscious. He later dies from burn injuries, either from the alien presence or the accumulating heat-related chaos.

The growing tension among island residents under the heat foreshadows their psychological deterioration.

Godfrey Hanson is a scientist from the mainland who arrives at The Swan already suspecting extraterrestrial activity. He rents a room and spends his time setting up motion-sensitive cameras and collecting soil samples around the island. His scientific background and preparation suggest he either suspected Fara was a target or had prior knowledge of the alien threat, though the film doesn't explicitly explain his inside information.

Hanson arrives precisely as the heatwave begins, and his secretive research activities predate the visible alien attacks.

The group attempts to lure the aliens with a bonfire of hay in a field, then drop dynamite to destroy them while using flare pistols to signal for help. The plan quickly fails during execution, Foster is killed first, then Hanson dies in the ensuing chaos. The aliens, despite being drawn to the fire and light, prove too dangerous and unpredictable for the ambush to succeed, resulting in multiple casualties before the survivors are forced to flee.

The aliens' extreme heat makes close-range detonation extremely dangerous, and their attraction to the flare pistols complicates the signaling attempt.

The aliens systematically destroy all communications on Fara. At the weather station, Ken Stanley and Gerald Foster discover the communications operator has been killed and all equipment destroyed. Additionally, the heatwave knocks out telephones and disrupts other means of contact. This isolation prevents the islanders from warning the mainland and ensures the invasion remains hidden from outside help.

The escalating attacks on individuals foreshadow the aliens' methodical cutting of all communication lines.

Dr. Vernon Stone, the island's physician, attempts to reach the meteorological station to contact the mainland about the alien threat. He is waylaid and killed by the alien presence before he can send any warning. His death removes a key character and eliminates the last hope for outside intervention, forcing the remaining survivors to rely on their own devices.

Stone's medical background and initiative make him a logical choice for seeking help, but the aliens have already sealed off all escape and communication routes.

Jeff Callum, Frankie Callum, Angela Roberts, and Ken Stanley survive the alien invasion. The final death toll includes Dr. Stone, Stella Hayward, Foster, Hanson, and others. The survivors make it through the crisis partly due to luck and the intervening thunderstorm that kills the aliens. Their return to safety is fragile and bittersweet, as they remain traumatized by the experience.

The buildup of casualties throughout the film creates uncertainty about which characters will survive until the storm arrives.

The aliens generate extreme heat as part of their biology or technology. Anyone who gets too close experiences immediate burning, the tramp dies in a cave from a high-pitched whirring sound and associated heat, sheep are found scorched from within, and Bob Hayward is attacked and nearly burned when his car catches fire after being heated by the alien presence. The heat acts as both a weapon and a defense mechanism.

Early incidents of burned animals and the tramp's death establish the lethal heat pattern before the aliens are explicitly identified.