During 4.09 "One Wedding and a Funeral", Mac discovers, that the 333 caller has been stalking him for some time, and at the end, a three-dimensional puzzle of his first case and first apartment in NYC leads him to where he got engaged in NYC. There he finds another puzzle with a stone leading him to a building back in Chicago. Mac also tests the puzzle pieces and the T-shirt and sees that whomever handled the puzzle was the brother of the T-shirt's owner. Mac flies to Chicago and the building from the puzzle. The episode ends with the 333 caller saying to him "How does it feel to be home, Detective Taylor?"