Will throws his annual Halloween bash, much to the dismay of Fiona and Marcus, who consider it one of their least favorite holidays. Despite the fact that Fiona believes Will has other motives for throwing the party, she ends up meeting Sean there and reveals a whole new side of herself. After a few mishaps at the party, Will shows Marcus the joys of Halloween.

Will is sued by an angry ex-girlfriend, Stacy, who is claiming she co-wrote his song "Runaway Sleigh." Will looks to Fiona for help in hopes that she can persuade Stacy to drop the lawsuit. However, things don't go according to plan as Fiona begins to sympathize with Stacy. Meanwhile, Marcus tries relentlessly to spark a run-in with bad girl Shea, as he continues in his quest for her affection.