While on holiday in Saltbottle, Grandfather and Roo stumble upon their old boat, the Unsinkable, now in ruins and up for sale. A mix-up at the auction leaves Roo as the accidental buyer—now they just need to pay for it!
A fishing trip to the Forgotten Sea seems like the answer, but when the boat sinks, Grandfather and Roo are stranded on a desert island. Their “Man Friday” turns out to be a film director staying in a nearby luxury hotel—and back at sea, the Captain has found both treasure and their beloved boat.