TERRA PROSPEKT a Combine high security penitentiary facility located near city 20 is known to be the last place where human rebels want to be. The last part of Collins story starts there.
At the end of Operation Rift, Gman saved Collins from the air strikes that destroyed the old Boomer town mines and he sent him to the future as "a chance of seeing the holocaust of the human race". Former corporal ended up in Terra Prospekt, as a prisoner of the Combine regime.
Collins has sworn something: HE WILL NOT LEAVE HIS BONES THERE!