Nightbirds on Nantucket — Joan Aiken

Having had enough of life on board the ship that saved her from a watery grave, Dido Twite wants nothing more than to sail home to England. Instead, Captain Casket's ship lands in Nantucket, where Dido and the captain's daughter, Dutiful Penitence, are left in the care of Dutiful's sinister Aunt Tribulation. In Tribulation's farmhouse, life is unbearable. When mysterious men lurk about in the evening fog, the resourceful Dido rallies against their shenanigans with help from Dutiful, a cabinboy named Nate, and a pink whale.