King Acrisius of Argos (Donald Houston) has his daughter Danaë (Vida Taylor) imprisoned in a tower, out of jealousy for her beauty. However, Zeus (Laurence Olivier), king of the Greek gods, impregnates her and the product of this affair is Perseus. Fearing that his grandson will one day grow up to kill him, Acrisius has both mother and child set out to sea in a wooden chest, in the hopes of killing them. However, out of revenge, Zeus has Acrisius killed and orders the sea god Poseidon (Jack Gwillim) to release the last of the Titans, a giant humanoid sea monster called the Kraken, to destroy Argos. Meanwhile, Danaë and Perseus miraculously survive and land on the island of Seriphos, where Perseus grows into a young man.