You are Adrian Shepard, in stassis since the debacle st Back Mesa (Half-Life: Opposing Force).
But fortunuate for you, a sitiation occurs and the G-man is forced to bring you out of stassis.
The events in this game happen before Gordon Freeman arrives to City 17 (Half-Life2).
You will start in a base simular to Black Mesa thats still resisting the combine occupation.
From there you will go to a quarry, sovjet submarine base and the basements of an early citadell where
the combine stumbled upon alien artefacts.
This game is influenced by Matthew Reilly's books wich were an inspiration to me.