Sorry if I'm a bit late here, and am being nitpicky. The title sounds great and all, but "Beneath the Mask" implies you play as a Combine soldier; when rather, Barney is a combine soldier but is actually a rebel in disguise as one, so it somewhat implies you're playing as one of the bad guys instead of the bad guy that's actually a good guy in disguise.
Could be a sabotage one? Storyline, Rebels are attempting to break out so barney has to go undercover as a combine. And whilst he appears to be acting as a combine soldier he is secretly trying to sabotage the combine defences to allow the rebels to get out of city 17