" Dennis and Dee Get a New Dad " is the tenth and final episode of Season 2 of It's Always Sunny in Philadelphia , notable for fundamentally shifting the Reynolds family dynamics and introducing key recurring characters. Key Plot Developments
: The episode ends on a major cliffhanger implying that Frank may actually be Charlie’s biological father , following a one-night stand with Charlie's mother, Bonnie, thirty years prior. [S2E10] Dennis and Dee Get a New Dad
: Mac and Charlie attempt to impress Mac’s imprisoned father, Luther McDonald , by trying to become hardened criminals. This leads to the infamous and absurd plotline where Luther asks them to smuggle heroin into prison via their rectums. " Dennis and Dee Get a New Dad