Off the coast of Spain in the Mediterranean, the DSV Alvin submarine finds a missing American hydrogen bomb.

Alvin (DSV-2) is a crewed deep-ocean research submersible owned by the United States Navy and operated by the Woods Hole Oceanographic Institution (WHOI) of Woods Hole, Massachusetts. The original vehicle was built by General Mills' Electronics Group in Minneapolis, Minnesota. Named to honor the prime mover and creative inspiration for the vehicle, Allyn Vine, Alvin was commissioned on June 5, 1964.

The Palomares incident occurred on 17 January 1966, when a United States Air Force B-52G bomber collided with a KC-135 tanker during mid-air refueling at 31,000 feet (9,450 m) over the Mediterranean Sea, near the Spanish village of Palomares in Almería province. The collision destroyed the tanker, killing all four crew members, and caused the bomber to break apart, resulting in the deaths of three of its seven crew members. The B-52G was participating in Operation Chrome Dome, a Cold War airborne alert mission involving continuous flights of nuclear-armed bombers.