Marshall Wheeler is student at Blake Holsey High and a main character in the series. He is passionate about science and loyal to all of his friends. Marshall is also sensitive and compassionate. He has a moral code of his own: he does not mind breaking the rules, however he is against lying and cheating. He believes that the perils and odd occurrences at Blake Holsey are best faced together, rather than different members of the Science Club acting on their own.
Despite this, Marshall sometimes feels unappreciated and ignored by others. On one occasion, these feelings manifest in Marshall becoming invisible. Much of this insecurity stems from his feeling eclipsed by his older brother, Grant Wheeler, who happens to be more popular, talented, good looking, and intelligent than Marshall. When Grant visits the school on the day of his job interview at Pearadyne, Marshall's feelings cause him (and eventually Grant) to take on properties of different elements in their ascending order on the Periodic Table.
A talented musician and keyboard player, Marshall becomes the frontman for the local three-piece rock band Magnet 360. Marshall is also an ambitious entrepreneur, selling modified cell phones and networking computers to raise money for college. Unfortunately, these attempts to earn some cash usually backfire rather badly. Corrine describes him as a person who is especially good at chemistry and somewhat of a hustler, but doesn't talk about his emotions often.
Marshall develops a romantic relationship with Corrine Baxter, but resents it when she tries to overschedule their time together. In another universe where Blake Holsey teaches the fine arts, Marshall's counterpart praises Corrine's "great look", and kisses her before she returns home. The incident teaches her to take a more relaxed, less regimented approach in her relationship with the Marshall of this universe.
After Josie Trent disappears down the wormhole and does not return, Marshall is taken out of Blake Holsey by his parents and placed in another school. However, he still maintains contact with Lucas and Corrine. He returns to visit his friends at their graduation and so is present when Josie returns, he is with his pals when Josie obliterates Avenir. When Corrine contemplates backpacking through Europe before attending university, he suggests that he join her, which Corrine welcomes.