Derek Mergen was a former member of the Marxist Radical Front and is the current leader of the Global Liberation Front terrorist cell in Olivet, France. A training compound for the cell was located underneath a brandy distillery in the town. Rainbow discovered the location of this compound after raiding a GLF terrorist base in the catacombs under Paris. Intelligence suggested that Mergen would be able to give Rainbow information on the GLF's next move. As such, Chavez, Lofquist, Pak, and Loiselle were dispatched to capture Mergen.
After fighting through the compound, Rainbow located Mergen. To their surprise, Mergen had been shot by his own men in order to prevent his capture by Rainbow. Despite this, he was still alive and was extracted, albeit in critical condition. He was then taken to an intensive care unit at a local hospital in Paris. After successfully stopping the GLF from assassinating Mergen, he was removed from the ICU and interrogated two days later. He revealed to Rainbow that the GLF would be taking part in an upcoming arms deal to purchase weapons for a major terrorist attack in Europe.
- While the PC version of Lockdown features the Global Liberation Front, it also features several terrorist groups that fill the same roles that the GLF has in the console version of the game. In the PC version, Mergen is the leader of a United Fatherland Brigade terrorist cell rather than a GLF cell. Additionally, instead of Mergen revealing a GLF arms deal during his interrogation, he instead reveals an upcoming arms deal with the Marxist Radical Front.