When Sam tells the kids the story of Pontypandy Pete's Treasure, Norman desperately wants to find it. Little does he know, that Joe's latest invention (a mini sub), will run out of power leading Penny and Sam to discover the sunken wreck of the Pontypandy Pearl. Professor Pickles from Newtown Museum comes to see all of the artefacts and in doing so, discovers Pontypandy Pete's log book. Inside, the Professor finds a clue that could lead him to the treasure? But Norman and Hannah manage to get a sneak peek at the clue as well and the race is on find Pontypandy Pete's Treasure.