The sirens who tempted Odysseus were not fish-tailed women at all; on ancient Greek pottery they have feathers, talons, and wings. This episode tracks how the mermaid got her tail, from the Old English roots of the word tied to the sea and servitude, through the 7th century Liber Monstrorum and a 13th century Bodleian bestiary whose text says bird while its illustration shows fish, to the medieval church turning the comb and mirror of Aphrodite into emblems of vanity and sin.

We then travel the globe: Mesopotamian kulullu guardians, the grief-stricken Syrian goddess Atargatis, 2,000-foot Norwegian storm monsters, the treasure-giving Ben Varrey of the Isle of Man, the Zennor mermaid of Cornwall, Africa's Mami Wata, and Philippine tales of the Cataw and a fateful milkfish bargain. Finally we look at Paracelsus's idea of soulless water spirits ...