In Warhammer 40,000: Space Marine you control the burly Captain Titus, a Space Marine for the Ultramarines sector and a veteran of many wars. An Ork horde has invaded an Imperial Forge World, one of the embodied planet-sized industries where war machines are being developed to assist in humanities fight against the riotous Ork race. Humans cannot lose this planet, but it’s just not that simple. An even darker evil is spreading through the whole of the planet. With the Imperials marching in to liberate the world, the Ultramarines are to stack up in vital locations until reinforcements arrive.