The Third Wheel is the seventh book in Jeff Kinney's Diary of a Wimpy Kid series. In this book, the protagonist, Greg Heffley, narrates his struggles in middle school as he tries to find a date for the Valentine's Day dance. As usual, things don’t go according to plan, and Greg ends up in awkward situations, particularly when he finds himself as the third wheel to his best friend, Rowley, and a girl named Abigail.

Greg's efforts to appear cool, navigate social dynamics, and fit in with his peers lead to hilarious and often embarrassing outcomes. The book highlights the theme of friendship, middle school crushes, and Greg’s misadventures, with Jeff Kinney’s signature humor and illustrations adding to the light-hearted, relatable tone of the series.