Play the first game for free ahead of the sequel's 2013 release.
Atmospheric FPS Metro 2033 can be yours at no cost if you head over to Facebook and like THQ's page.
You'll be promoting the new Metro: Last Light game to your friends by doing so, with the free game download being your reward.
Once you've liked the page you'll be sent a code – while supplies last – which can be redeemed on Steam.
Alternatively you can snap up the rather great Humble THQ Bundle, which includes Metro 2033 and a host of other games.