Unsavory characters have been spotted in the park.Earthquakes have been disturbing the house. Pops's sockdrawer has been pilfered. Yep, it's mystery time. Whentrouble settles over the park along with the chill of winter,it's up to Rigby, Mordecai, and the rest of the crew tofigure out who's behind--or below--the disturbances.