Soldier of Fortune II: Double Helix is a video game created by Raven Software, a sequel to Soldier of Fortune. It was developed using the Quake III: Team Arena engine. Once again, Raven hired John Mullins to act as a consultant on the game. Based on comments and criticisms of the original game, Raven Software developed Soldier of Fortune II to be a more "realistic" game, with tactical shooters like Operation Flashpoint: Cold War Crisis and Tom Clancy's Rainbow Six as inspirations rather than Quake. A sequel titled Soldier of Fortune: Payback, made by Cauldron HQ was released for Microsoft Windows, PlayStation 3 and Xbox 360 in 2007.
The theme of the sequel is germ warfare, as the mercenary Mullins and his new partner Madeline Taylor travel to Colombia to investigate a viral outbreak in a small town, only to link it to a shadowy organization called Prometheus. The virus, called Romulus, is followed by a computer virus called Remus which is programmed to delete files on any computer in the world, in this case, files relating to Prometheus and Romulus, so an anti-virus cannot be formulated. Prometheus then plans to blackmail the G8 countries at a summit in Switzerland for billions of dollars. It is revealed throughout the course of the game that a mole inside The Shop may be feeding information to the terrorists.
- John Mullins: Born and raised in Southwest Oklahoma, Mullins served three tours in Vietnam, earning three Purple Hearts. He was also a member of the controversial Phoenix Program group created to assassinate high ranking Vietcong officers. Mullins retired from the military to become a "consultant", or mercenary, 12 years ago. He now takes jobs from the United Nations anti-terrorist group called The Shop. With a medium build, Mullins boasts strength and speed that few men possess. John Mullins is voiced by Todd Susman.
- Madeline Taylor: With the death of John's lifelong friend and partner, Hawk, The Shop looked long and hard for a suitable match to John's can-do attitude. Although a fully trained field agent, Taylor's specialty is human medical research, making her an invaluable ally in the fight against chemical and biological weapons. Madeleine Taylor is voiced by Iris Bahr.
- Sam Gladstone: A 62-year old bearded book store owner and part-time employee of The Shop. A Captain in Vietnam, Gladstone excelled at recon, later spending several years with the CIA. He owns the small enterprise known as Goldberg's Used Books. Behind the old bookshelves however lies a hidden lab filled with the latest technology and weapons. Sam Gladstone is voiced by Earl Boen.
- Dr. Piotr Ivanovich: One of the Soviet Union's top Biopreparat scientists, Dr. Ivanovich has worked on chemical weapons for a very long time. Unlike his cohorts however, he wants out. Ivanovitch has extensive knowledge in his head which certain terrorist groups would kill for, and he has passed most of this knowledge on to his young protege, Dr. Dmitry Sestrogor. Dr. Piotr Ivanovich is voiced by Alan Oppenheimer.
- Dr. Dmitry Sestrogor: A mysterious figure, Dmitry Sestrogor has been behind the production of many deadly bio-weapons which have been used throughout the world. This man, however, is no criminal mastermind. Held hostage by the ruthless Prometheus group, Dr. Sestrogor has been forced to develop deadly weapons in exchange for his life. Dr. Dmitry Sestrogor is voiced by Michael Bell.
- Anthony Michaels: The Shop's director, Michaels operates under the strictest of secrecy. For years he has pushed The Shop forward, hoping to bring terrorism under control. Michaels is an extremely powerful figure in his own right, being the head of an organization that owes no allegiance to any government and having a vast network of informants and agents across the world. Anthony Michaels is voiced by Cam Clarke.
GameplayThe series' focal point, graphic depiction of human bodily dismemberment, makes another appearance in Soldier of Fortune II. GHOUL 2.0, as the new engine was called, features 36 gore zones, allowing for increasingly detailed depictions of gore and carnage.
In contrast with the first game, Soldier of Fortune II has a more diverse number of real-life weapons. Several of the weapons can have special attachments such as a laser sight. In the single player campaign, it is also possible to have mixed akimbo weapons.
Unlike the original game, there are no futuristic weapons or sci-fi elements. The most advanced weapon encountered is the OICW, which is based on a former weapon prototype of the United States military.
In multiplayer mode, there are five gametypes: team deathmatch, infiltration (reminiscent of Sega's game 005), capture the flag, deathmatch, and elimination. Additionally, the 1.01, and 1.03 patches for the game introduced the demolition and VIP gametypes. Demolition most closely resembles Counter-Strike gameplay because of its round-based nature and focus on bomb planting/defusing. In demolition, elimination, and infiltration modes, gameplay takes place in rounds, and players cannot respawn when killed until the end of the round.