It's Always Sunny in Philadelphia: Season 8, Episode 6

8 - 6: Charlie's Mom Has Cancer

In perhaps the most depraved scheme of them all, The Gang rallies around Charlie's mom as she battles cancer. As Mac, Charlie, and Dee struggle with their faith, Frank loses his memory and his mind in a quest for buried treasure, and they're all rocked by a revelation that will shake Paddy's to its very foundation!