Evan Gallico visited the San Jose St. Bonaventure hospital after tripping "over his own feet" and breaking his arm during a field trip. Shaun notices the boy and sees that he bears a striking resemblance to Steve Murphy (Shaun's late younger brother). Shaun decides to meet the boy under the pretenses of giving him a checkup. He notices that Evan has trouble moving his eyes, and asks if he hit his head when he fell. Evan says no, so Shaun orders a head CT. On the CT, he finds that Evan had a tumor behind his inner ear and that it is affecting his balance (which explains why he fell). When Shaun talks to Evan's parents, he finds that Evan's been diagnosed with stage 4 osteosarcoma and has a year to live. The diagnosis was seven months ago, leaving Evan 5 months to live. Shaun also discovers that Evan's parents haven't told him about the surgery.
When Shaun goes in to remove Evan's cast (to put pins in his arm to hold the fracture in place) they get in a discussion about lying. Shaun asks how to know when to lie, and Evan says: "When people need to know things, they need to know. When they don't, lie through your teeth and feel good about it!" Shaun decides that he needs to tell Evan about his cancer, and finds out he already knows. According to Evan, his parents took him to the doctor for a sore leg. They did a bunch of tests, then told him he was fine, and to go home. The next day, his parents bought him a PS4. Evan got suspicious and googled his symptoms. (Seriously, don't do that. Google is not a reliable diagnoser.) He narrowed it down to Osteosarcoma or growing pains. His parents had bought him a PS4, and they don't do that for kids with growing pains, so he knew it was osteosarcoma. He then tells Shaun that it's fine, he isn't scared of dying. Besides the fact that it'll suck if it hurts, he's not scared about After. Shaun asks if it's because he believes in heaven, and Evan answers No, it's because he doesn't. That when it's over, it's over, and there's nothing you can do.
Shaun does a lot of research and discovers that Evan might have been misdiagnosed, and might have Langerhans cell histiocytosis instead, which is curable. To find out if he was misdiagnosed, Shaun needs to do a bone marrow aspiration. Instead of giving Evan and his parents false hope, while doing the test he lies and says he saw a low RBC count and wants to find the cause. Evan knows he's lying, and Shaun ends up telling the truth, but before he can do the bone marrow aspiration, Evan's parents come in. After finding out Shaun told Evan about his diagnosis, they throw him out of the room. Then Evan starts coughing blood, and is close to hemodynamic collapse. They go directly into surgery, knowing that if they wait too long Evan will die. They finish the surgery and are about to suture Evan when Dr. Brown notices he has lesions on his ribs, a sure sign that he has osteosarcoma, and that it has spread to his chest cavity.
After his recovery from the surgery, Shaun goes in to see Evan. Evan thanks him, and he apologises for being wrong. Shaun asks if he can read Evan the last three pages of 'To Kill a Mockingbird'. Shaun bids Evan farewell with tears in his eyes by reading him three pages from the book he gifted Steve on his birthday. He reads Evan the pages that Steve didn't finish reading before he died, and thanks Evan, saying farewell forever.