Marcus has a whole new spring in his step. Now that his mom has a job, he's got his own house key, and every day after school, he's home alone! Fiona's worried, so Marcus keeps in touch by phone, assuring her he's fixing a nice healthy snack. But just as he's cutting into his orange, the knife slips right into his foot! Rather than tell his mom, Marcus hollers for Will, who races him to the ER screaming, "I need a doctor!" He's about to deliver Marcus into the arms of a medical professional, when he spots Dr. Sam Lake - a HOT doctor. This emergency just became an opportunity to hook up. Singing Will's praises, Marcus discloses he's a famous songwriter. When Sam steps out, Will lays down some down low: they never EVER talk about "Runaway Sleigh," because he's not that kind of songwriter. Dr. Smoke Show needs to think he's cool. When Sam returns, Marcus immediately tells her Will has written songs for supercool guys, like... Michael Bublé. Luckily, Fiona blows in with all her neuroses, sending Sam running. Will follows Sam, laying it on thick. He's amazed when Sam cuts to the chase. She's blunt when she's tired, and no, she's not going to have sex with him, even though he looks kinda good.
After Marcus is safely home, Will tells Andy all about Sam. Laurie has a warning for Will: he's already lied about writing for Bublé, and women like honesty. It's 2:00 a.m. when Will feels the need to tell Sam the truth, but she steamrolls him, asking him to sing her a song. Will performs a song by Rivvrs - making Sam think he wrote it - and the couple heads out for a late night burger, hitting it off. They almost share their first kiss in a paddleboat! The next day, Will shows Andy his criteria for the perfect girl, written down by his 10-year-old self. By this definition, Sam is the perfect girl for Will! Marcus pops in for advice on his latest problem: after the knife in the foot incident, Fiona is watching his every move, literally, on Skype.
On his follow-up visit with Sam, Marcus tells Sam that his mother has been in a guilt spiral since the accident and is Skyping his every move. When a lovestruck Sam claims Marcus is lucky Will was home to bring him to the hospital, Fiona blows Will's cover. He's just a lazybones and Fiona doubts he writes songs for Bublé and Rivvrs. On a date with Will, Sam tries to get to the bottom of it, urging Will to sing her one of his original songs. When he sings her a song about random objects in the room, Sam stomps out, but not before Will tells her that he doesn't write songs for Bublé or Rivvrs.
Later, Marcus finds Will poised to burn his Perfect Girl notebook on the barbeque. Marcus thinks Will is perfect the way he is - albeit messed up and flawed. Clearly, if Sam truly is the perfect girl for him, she'll come around. In thanks for this wisdom, Will shows Marcus how to set up a Skype loop, so Fiona just sees him doing homework - until she realizes the video is looping. That's when Will pops into Fiona's office with Marcus, who explains he's not her little baby anymore, he's her prepubescent tween. Hugging the oxygen out of him, Fiona apologizes for holding on too tightly. Will proceeds to the hospital to tell Sam the truth. He wrote "Runaway Sleigh" eight years ago, and he hasn't written anything else because he's scared it won't be any good. Hoping for another chance, Will picks up his guitar and sings "Runaway Sleigh," winning a smile and getting the entire waiting room to sing along.