The Herring Fleet Hoax

You arrive at the captain's table aboard the RMS Bellerophon, three days out from Southampton, where the sherry is flowing, the napkins are pressed to a razor's edge, and someone has apparently swapped a two-million-pound seascape for a very convincing Sunday painter's daydream. The captain has confined last night's collector's evening party to their cabins pending your arrival. Time to find out who forged history somewhere between the fish course and the trifle.
Sometime between the pre-dinner sherry reception and the serving of dessert, Lady Ashworth-Kane's Turner-attributed seascape 'The Herring Fleet at Dawn' was switched for a forgery while locked in its display case in the ship's Verandah Gallery. The theft was discovered at 9:15pm when she unlocked the case to show a boarding Sotheby's representative the piece and noticed fresh glue at the frame's corner and a signature sitting a fraction too high. Only two keys to that case existed all evening: Lady Ashworth-Kane's own, worn on a chain, and the one issued to the voyage's appointed restorer.
Victim: Lady Priscilla Ashworth-Kane — A formidable widowed art collector sailing to Gibraltar to sell her prized seascape at auction.

The suave restorer hired to authenticate the painting, remarkably unbothered for a man whose life's work just went missing.
“I was seated at the captain's table for the entire dinner service, digesting my turbot and minding my own business, until the commotion over the painting broke out.”

The head stewardess who served every course that night and remembers absolutely everyone's business.
“I was running back and forth between the galley, the cellar, and the table all evening, same as any dinner service, love.”

The ship's nervous chaplain, who slipped away from dinner twice that evening for reasons he'd rather not discuss.
“I stepped away briefly to look in on a seasick passenger, Mrs Higgins, and said a few prayers over supper - nothing more sinister than that, I assure you.”

The collector's niece and companion, fiercely protective of her aunt and oddly touchy about the family finances.
“I sat with Aunt Priscilla the whole evening, as I always do - someone has to keep her wine glass from running dry and her stories in check.”