An alternate ending to the original Innocence turned Killer timeline.
Riley was the only person to survive Rusty's massacre. Albeit, just barely, seeming permanently damaged. With Rusty not reversing time like in the original timeline and ultimately killed by the enemy he thought he had killed, Riley is the only person left alive on the island, meaning being lonely.
Many months have passed, and now he has adapted to this new loneliness. However, reuniting with someone and diving back into his pasts, gives Riley the chance to return everything to as close to normal as possible.