Martin a career criminal with OCD, only steals items that won’t be missed. Food, cleaning supplies, and higher end pieces, like jewelry that hasn’t been used or silver. He likes his “clients” and when he accidentally knocks a toothbrush in the toilet, he is unable to just wash it off, but rather replaces it, which leads him to his first good deed. He begins to think that maybe he is meant to be in these houses for more than personal acquisitions.
Something missing refers to both the items in people’s homes as well as relationships in Martin’s life.