Gup the Sailor and the Devil to Pay - Marek M Jenai - Bog

Now that Gup has reunited with his family, he has earned an honored place among an elite and secret band of royal privateers. Joined by the ragtag crew that aided him since the beginning, and with Hettie by his side at the helm, Gup can now follow in his father's footsteps and his orders on a ship of his own. Named after the vengeance his Cannibal first mate still seeks against their enemy, Gup and crew return to the sea, and seek to take down the pirate Captain Keelhaul once and for all. But the Siren's Eye that the pirate wields boons a peril Gup could never imagine!
Though they still have an alliance with the merpeople, Gup and his mateys, along with his parents and their crew, begin to realize that finding the villainous captain will take them through unexpected twists and turns across the known waters of their world. Coming face-to-face with new creatures, potential allies, and even greater scoundrels than the pirate they seek, can Gup succeed in his quest? Will he prove himself worthy of the captaincy, or will Gup realize his position as a privateer captain was a grave mistake?