Soldiers are crowded around screens watching for victory. No, it's not a news broadcast: each of the screens shows a different world, a different reality, and a different way for a battle to play out between a gunsuit containing Cassandra "Potts" Potter and massive biomechanical monsters. These monsters have come through wormholes all over the globe from an alternate evolutionary timeline. Time after time Potts watches herself die, until miraculously one day the crew discovers a sequence where she stabs a monster with a giant spike, and wins.
Potts immediately mans her mech and dives through a portal to the corresponding world, where she almost loses a battle against a monster before her alternate self saves her via spike. They are two different versions of the same woman, brought to their respective positions from years of evolution and personal choices. Potts' other self introduces her to a crew called the Tombstones, who are in the slightly earlier stages of defending their base from the tentacled bio-mechs and actually possess a refridgerator full of beer. Potts might be optimistic for the first time in years...
... until a new kind of bio-mech appears. One smaller than a cockroach but completely lethal. And swarms of them are about to storm the base. Is this new universe the solution, or just another path to destruction?