In the pilot, it's established that Fiona is Irish. As such, she speaks with an Irish accent. In the second episode, she greets Michael using an American accent. When he asks her about it, she says she "can't go around Miami sounding like a freaking leprechaun". Later, it's determined that in order to hide from her numerous enemies, she took on an American accent. In the episode Long Way Back, season 3 episode 9, her brother Sean discusses her accent change briefly with her. In one episode, Fiona says "new country, new accent".