"The game follows John Jack, a professional killer recruited by H.A.R.M., a criminal organization central to the No One Lives Forever series. Contract J.A.C.K. (Just Another Contract Killer) is set between No One Lives Forever and No One Lives Forever 2. The game does not involve UNITY, the organization for which Cate Archer works and that opposed H.A.R.M. in the other two games. Rather, J.A.C.K. pits H.A.R.M. against a rival criminal organization, Danger Danger.
Source: Wikipedia, "Contract_J.A.C.K.," available under the CC-BY-SA License.