The Pirate Treasure is a wooden chest filled with rare and priceless artifacts dating back to the 16th Century, which was once owned by Captain Calles. The treasure is now on display at the Sodor Museum.
During the 16th Century, Captain Calles became notorious for sinking merchant ships and stealing their valuables, keeping their goods for himself as his treasure. Eventually, the Merchants and the Navy teamed up and began tracking Calles down, who sailed his ship into a cavern open to the Irish Sea and buried the treasure close to Arlesburgh. Captain Calles drew a map so that he could find the treasure again, but somehow lost it.
Over four centuries later, Marion found the treasure chest when she was digging a new cutting for the construction of the Harwick Branch Line. Marion believed that it was simply a wooden box, but when she met up with Thomas, she accidentally dropped the chest on him, causing the chest to bust open and revealing its contents. After he was made aware of the treasure, the Fat Controller made plans to donate the treasure to the Sodor Museum, and kept the chest locked away in a safe at Knapford until he could deliver it to the Museum.
However, Sailor John, who had been desperately searching for the treasure, found out where the treasure was being kept, and arrived at Knapford to destroy the Fat Controller's office and steal the treasure for himself. Thomas chased after Sailor John and Skiff in an attempt to stop them from getting away, but was unable to prevent them from escaping when he fell into the sea. Sailor John tried to sail back home with the treasure, but the chest was too heavy for Skiff to carry, and after Skiff was capsized, Sailor John lost the treasure when it sunk to the bottom of the sea.
After Sailor John was arrested, the treasure chest was recovered by a group of scuba divers, who had the treasure taken to the Museum.