In Dollhouse, the Actives are regular people who have had their personalities wiped clean so they can be programmed, for their own reasons, with specific skills and personalities. They can be the perfect companion, spy, or even assassin.
But one specific Active, "Echo", has a secret. She is no longer just a blank slate waiting for her next assignment. Echo is remembering flashes of the lives that she has lived and the games she has played, and she is starting to wonder just who she really is.