A suspected bomb left on Stella’s car is discovered to be a box full of puzzle pieces stained with blood. The pieces are formed into the shape of a ticking clock. As the CSIs put the pieces together, Mac realizes the puzzle is of a building significant to his own life and this could be the work of the mysterious “333” caller who has been stalking him since his trip to London. When a second puzzle turns out to be the Tribune Tower in Chicago, Mac’s hometown, Mac has no choice but to get on the next flight to Chicago to solve the biggest mystery of his life. Meanwhile, the CSIs get an unceremonious invitation to the wedding of the year in Central Park when the groom is found dead and the wedding party and guests are engaged in the most absurd brawl ever.
