Brett, Janice, Jason and Henry were survivors that tried to break into the MESA Pharmaceuticals inc. warehouse to get the drugs stored there but the zombies there were too fast (due to Ritalin exposure) for them. One of their members, Jason (Janice's husband), was bitten and zombified.
A month later, they encountered the Westward-bound survivor group.
Hotly pursued by the heroes, Brett and his group forced Murphy helped them break into the drug warehouse. Their obsession with stealing the drugs lead to their ultimate demise.