Using a modified Quake II engine, the game features a mix of a third-person camera with a first-person shooter's action, making for a new gaming experience at the time. While progressive, this was a controversial design decision among fans of the original title, a well-known first-person shooter built on the Doom engine. The music was composed by Kevin Schilder. Gerald Brom contributed conceptual work to characters and creatures for the game. This is the only Heretic/Hexen video game that is unrelated to id Software, apart from its role as engine licenser.
Players control Corvus from a fixed camera in 3rd-person perspective. Players are able to use a combination of both melee and ranged attacks, similar to its predecessor. Defensive spells are also available, and they draw from a separate ammunition pool. The game consists of a wide variety of high fantasy medieval backdrops to Corvus's adventure. The third-person perspective and three-dimensional game environment allowed developers to introduce a wide variety of gymnastic moves, like pole vaulting, in a much more dynamic environment than the original game's engine could produce. Both games invite comparison with their respective game-engine namesake: the original Heretic was built on the Doom engine, and Heretic II was built using the Quake II engine, later known as id Tech 2. Heretic II was favorably received at release because it took a different approach to its design.
After Corvus returns from his banishment, he finds that a mysterious plague has swept the land of Parthoris, taking the sanity of those it does not kill. Corvus, the protagonist of the first game, is forced to flee his hometown of Silverspring after the infected attack him, but not before he is infected himself. The effects of the disease are held at bay in Corvus’ case because he holds one of the Tomes of Power, but he still must find a cure before he succumbs.
His quest leads him through the city and swamps to a jungle palace, then through a desert canyon and insect hive, followed by a dark network of mines and finally a to a castle on a high mountain where he finds an ancient Seraph named Morcalavin. Morcalavin is trying to reach immortality using the seven Tomes of Power, but he uses a false tome, as Corvus has one of them. This has caused Morcalavin to go insane and create the plague. During a battle between Corvus and Morcalavin, Corvus switches the false tome for his real one, curing Morcalavin’s insanity and ending the plague.