The cartoon is based in the "Land of Ooo", formerly New York. Leonard, a 17 year old survivor and former member of the Order 66 - Dissavowed, got his hand cut off during the Great Mushroom War. Once he reached safety he grows a demon hand and met Finn the Human, who was thought as Leonard's 16 year old brother. Together, they have to defeat Simon "Ghost" Riley, Jason Voorheers and their most feared target... Death.
YOU LAZY NO GOOD SLACKERS! YOU DRIVE ME NUTS! CAN'T YOU JUST LISTEN TO ME ONCE IN YOUR WORTHLESS LIVES, BECAUSE IF YOU DID YOU WOULD SEE THAT I AM TRYING TO TEACH YOU SOME SIMPLE RESPONSIBILITY! SOME PRIDE IN YOUR WORK, AND A JOB WELL DONE! BUT YOU WOULDN'T KNOW A JOB WELL DONE EVEN IF YOU PAID SOMEBODY TO DO IT FOR YOU, AND THEN YOU WOULD SCREW IT ALL UP ON THE ACCOUNT THAT YOU CAN'T EVEN FOLLOW THE SIMPLEST OF INSTRUCTIONS! WORRYING MORE ABOUT BEING COOL THAN DOING YOUR JOB! - Leonard shouting at Jason Voorheers