The Cleaner is a man who disposes of bodies known for liquifying the corpses.
Alice and Rhys, to find out what had happened the night he shot Felicity and who saved her, tracked down The Cleaner and set up a fake death. Rhys posed as the corpse and once The Cleaner was in the room, Alice confronted him and started asking questions. When he saw that Rhys wasn't really dead, he fainted. Once he was awake, they questioned him about that night. He initially claimed he'd done his job as directed, but when pushed, he admitted that by the time he arrived that night, the body was already gone, so he took the money and fled.
He used to do corpse disposal for the Kensington Firm. His specialty is liquifying corpses so they can be put down the drain. He left the Kensington Firm after going to clean up Felicity's body only to discover it wasn't there anymore.