The Merman and the Pirate

In this version of the Little Mermaid, merman Arien gives up his voice to gain legs in order to repay a debt.
Arien enjoyed his quiet life in the world's oceans. He had no interest in the cold-hearted, crass humans until his little sister was accidentally caught in the nets of the Coral Queen and released by the schooner's kind-hearted Captain.
Pirate ship Captain Molly Obsidian is on a mission to make an alliance with the governor of the Castillo de San Marcos when she finds a stranded male on a makeshift raft. Rescuing him, she hopes she hasn't put her crew or her mission in danger.
With time running out, unlikely alliances and surprising betrayals lead up to an explosive conclusion.