Landing on an island surrounded by a sea of acid, the TARDIS is captured by Arbitan (George Coulouris), the Keeper of the Conscience of Marinus. If the Doctor (William Hartnell) and his friends intend to reclaim the TARDIS, they must collect four of the five keys needed by Aribtan to keep his Consience machine working. Much against his better judgment -- after all, the Conscience is a despotic entity, holding an entire planet in bondage -- the Doctor agrees to retrieve the keys. Written by Terry Nation, "The Sea of Death" originally aired on April 11, 1964, as the first episode in the six-part story arc "The Keys of Marinus." ~ Hal Erickson, Rovi