Peter Wilkes, tired of his connection with a disreputable secret order, requests its officers to release him from membership. He is released from further allegiance to the association upon the condition that he surrender to it any legacy that he might inherit. Shortly after this Wilkes learns that a firm of lawyers are advertising for him. In an interview with the lawyers, Wilkes is told that he is the next kin to a deceased nobleman and has inherited a sealed casket and a packet of papers. Wilkes finds the casket to contain valuable jewels and directions for locating additional treasure at Richmond Castle. Wilkes is now worried by the terms of his agreement with the order and decides to keep his wealth secret and ignore his promise. The attorney, although satisfied with the proofs which Wilkes produced, is nonetheless uneasy, and engages Grace Carter, a woman detective, to shadow Wilkes. Wilkes gains admission to Richmond Castle by posing as an artist interested in the interior, and while he is being conducted through the Castle, Grace Carter arrives unobserved. She disguises herself in an old court costume and assumes the pose of a wax figure, which stands in the hall of the Castle. Thinking himself alone, Wilkes presses a secret spring, which causes the fireplace to roll aside, revealing a flight of steps to the vaults below. Followed by the detective, Wilkes proceeds to the vaults and discovers his treasure. After exciting experiences, Wilkes returns home, where Grace Carter calls upon him, and asks why he acts in such a suspicious and secretive manner if he is the legitimate heir. Wilkes gives the detective details of his previous connection with the order, and she promises to bring his members to account. A messenger is ushered into Wilkes' study and reveals his identity as a member of the order. Wilkes escapes, and fearing that the society will again attempt to harm him, decides to live in a hotel. Grace Carter pays him a visit next morning and together they plan to capture the conspirators. From the window Miss Carter sees two members of the society approaching the hotel. She dresses in one of Wilkes' tourist suits, while Wilkes secretes himself. The detective climbs through a window to an adjoining roof and the members of the order thinking she is Wilkes, give chase. Racing across roofs, climbing chimneys and stacks, making hazardous jumps from roof to roof, sliding down a crane, jumping from a high bridge onto a passing motorboat, the detective finally escapes in an automobile. Late that night, a boat is seen making its way swiftly down the river to the back of an old wharf. Those aboard the boat climb through an opening, and cautiously make their way to an underground room, where the members of the order are gathered. A short, sharp fight ensues, but all the members of the order are captured, handcuffed and led away to suffer the penalty of their crimes. A few weeks later Peter Wilkes is married to Grace Carter in the ivy-covered church attached to Richmond Castle. The happy pair assemble with their guests in the hall of the Castle, where glasses are filled and toasts ore drunk to the future happiness of the bride and groom.