Renegade by J A Souders
When Gavin Hunter, a Surface Dweller, accidentally stumbles into Elysium's secluded little world, Evelyn comes to a startling realization: Everything she knows is a lie. Her memories have been altered. Her mind and body aren't under her own control. And the person she knows as Mother is a monster. Together with Gavin she plans her escape, only to learn that her own mind is a ticking time bomb...and Mother has one last secret that will destroy them all.