The airship Nautiflyus, piloted by the famous hero Captain Lamat, was on its way to deliver the wondrous Green Pearl to the city of Calli, in hope of curing its inhabitants with the Pearl's healing powers. However, when taking a shortcut through the so-called Forbidden Zone, the Nautiflyus crash-landed; both Captain Lamat and the Green Pearl were abducted by unknown creatures. The four crew members - the cartographer Julia, the strategist Ike, the engineer Maxx, and the archbishop Solaar - must deal with the new dangers, rescue the Captain, and retrieve the Pearl.
O.D.T. is an action role-playing game with some platforming and puzzle-solving elements. The player can choose to control any of the four characters. Each of them has his/her own strengths and weaknesses: for example, Maxx has high defense, while the archbishop has access to powerful occult techniques. Defeating enemies rewards the player with experience points, which can be used to increase a particular parameter of a character, increasing his/her combat abilities.