Lord Arthur Mullrine organises a party to celebrate the fiftieth anniversary since his business partnership began with the late Dr George McDee. During the party, time rolls back fifty years and guests who were not alive at that time are systematically murdered. The late Doctor McDee arrives at the party and Sapphire and Steel realise that the events of the night of his death are beginning to recreate themselves. It transpires that McDee had invented a lethal virus that could destroy all humanity. However, before this could happen he was shot by a jealous lover. Time has occupied the body of the lover and is attempting to arrange events such that McDee survives to accidentally unleash the virus. Sapphire and Steel ensure that he is, indeed, killed by the lover and his body and the virus are consumed in a fire. (thetvdb.com)