The Grand Splash
Mark originally made his debut at Seattle Grace amidst a scandal involving him, Derek, and Addison. While living in New York, Derek was married to Addison and Mark was one of his close friends. Mark ended up falling for Addison and subsequently had an affair with her. Fast forward to the time when Mark was living in New York and Derek and Addison were living in Seattle. Mark wanted to be with Addison and mend his friendship with Derek. He flew to Seattle to do just that, but it didn't exactly work as well as Mark had hoped. He went back to New York without Addison or Derek's friendship. Mark's not the type of guy that would let a little something like rejection keep him from the treasure at the end of the rainbow. That's what prompted this doctor to throw caution to the wind, leave his practice in New York, and set up shop in Seattle even after this initial rejection.