Raven's Peak - S4.E4

Robin and his band are at a masquerade ball, when Robin's old friend Tom enters, terrified and beaten. He is being chased by Vashon, the captain of Lord Holden's guard. Vashon accuses Tom of murdering Holden and his family. Robin defends Tom, but Vashon will not listen. In the ensuing fight with Vashon, Robin and his gang escape, and learn that Lord Holden is still alive. Vashon is actually pursuing Tom because he holds the key to an invisible cloak with magical powers. With Lord Holden's help, Robin and his companions defeat Vashon and return the cloak to a cave where it will be forever beyond reach.