Screenplay by DONALD JAMES   Directed by ROBERT ASHER     The Champions go to sea on a macabre trip to reconstruct the voyage of a nuclear submarine which has been found with its entire crew dead.     The U.S. nuclear submarine Kepple, which has been on a round-the-world voyage, is found drifting off the Irish coast with her entire crew dead. The cause of death is a mystery.   What strange tragedy has hit the vessel? The three Nemesis agents Craig (STUART DAMON), Sharron (ALEXANDRA BASTEDO) and Richard (WILLIAM GAUNT) are selected to go aboard when the Navy decides to reconstruct the Kepple’s voyage.   They are able to estimate the approximate area where the deaths probably took place, but there is plenty of drama before they reach this area, part of which is caused by the discovery of a newspaper reporter, Stantin (JAMES MAXWELL), who has smuggled himself aboard in the guise of a sailor.   Damaged through striking an uncharted underwater-reef, and, with the radio out of order, the submarine surfaces close to a strange island. Craig and Richard go ashore with two seamen. The island is apparently devoid of life, but there is a thin green mist in the air. The two seamen drop dead; Craig and Richard slump unconscious to the ground and then find themselves prisoners of a dedicated but ruthless scientist named Minoes (MARNE MAITLAND) who, working underground, is experimenting with a new type of poison gas which leaves no trace.   It now becomes clear that the Kepple’s crew became victims of the gas when the submarine came across the island; but Craig and Richard are beginning to wonder if they will ever be able to make their report. Minoes, worried because they have been able to survive, prepares to pump more gas into the sealed chambers in which they are captive. Richard is to be gassed first, but he manages to break out of his cell via an air conditioning shaft. When Minoes enters, he himself is gassed as he and the reporter Stanton, who has followed the Champions to the island, fight for possession of the one gas mask available.   Craig, too, has succeeded in escaping. But as he and Richard are about to leave, they find themselves in a bitter fight with Stanton. The outcome is that even the super-human qualities of the Champions are in danger of being unable to resist the lethal gas...     AN PRODUCTION   Series created by Monty Berman and Dennis Spooner   © Copyright Incorporated Television Co. Ltd. MCMLXVII     Stuart Damon   Alexandra Bastedo   William Gaunt   Anthony Nicholls   Paul Maxwell     Craig Stirling   Sharron Macready   Richard Barrett   Tremayne   Captain Baxter     Warren Stanhope   James Maxwell   Marne Maitland   Esmond Knight   David Blake Kelly   Rio Fanning     Admiral Parker   Stanton   Minoes   The Minister   | Lighthouse Keepers     Associate Producer   Director of photography   Art director   Editor     Johnny Goodman   Frank Watts   Charles Bishop   Peter Pitt     Musical director   Theme composed by   Post-production supervisor   Production manager   Casting     Edwin Astley   Tony Hatch   Philip Aizlewood   Malcolm Chistopher   Judith Jourd     Sound editor   Sound recordists     Music editor   Associate art director   Set dresser   Construction manager     Alan Corder   Len Abbott, Dave Bowen   Deveril Goodman   John Graysmark   Brian Rider   Bill Greene     Second unit director   Second unit cameraman   Camera operator   Assistant director   Continuity   Special effects     John Hough   James Allen   John Winbolt   Ken Baker   Valery Norman   Sid Pearson     Scenic artist   Production buyer   Make-up supervisor   Hairdressing   Wardrobe supervisor   Supervising electrician     A.J. Van Montagu   Sid Palmer   Gerry Fletcher   Michael Jones   Laura Nightingale   Ted Hallows       Made on location and at ASSOCIATED BRITISH ELSTREE STUDIOS ENGLAND.