Luc is first seen after Joan Watson decides to move out of her apartment and back into The Brownstone. Sherlock has arranged for Luc to move Watson's items even though she's hired movers. Holmes says that he only trust Luc to move the items into the Brownstone. Luc doesn't respond to any of Watson's comments so Holmes explains that he doesn't speak english and rarely speaks at all which Holmes says is one of Luc's many virtues. ("When Your Number's Up")
Holmes next uses Luc to tail Shinwell Johnson in order to prove to Shinwell that he does not have the skills to be a confidential informant (CI). Luc is able to follow Shinwell for nearly a day without being discovered. Once discovered, Luc takes a cab to the Brownstone and was waiting for Shinwell's arrival with Holmes. Holmes is adamant that Shinwell not be a CI to which Shinwell says he'll think on. ("Pick Your Poison")
Luc follows Shinwell.
Holmes has Luc help him move various furniture items in the Brownstone onto the roof to recreate a biker gang's headquarters in order to plan stealing a computer with the gang's dealings on it. ("A View with a Room")