Justin Clarke and Marissa Clarke are the protagonists of the forty-seventh Goosebumps book, Legend of the Lost Legend. While the book is told from Justin's perspective, Justin and Marissa are given almost equal development.
Justin Clarke is 12 years old, while his sister, Marissa Clarke, is 11. The siblings were taken to the small European country of Brovania by their father, who is searching for the Lost Legend, an illusive document, rumored to be encased in a silver box and located somewhere in the forests of Brovania. The kids end up separated from their father and following a dog to a cabin in the forest.
When the siblings enter the cabin, a large woman named Ivanna greets them and says that, in order to win the silver chest, the children will need to pass a test of survival in the Fantasy Forest. Ivanna also introduces the kids to Luka, a human-like creature that's covered in fur. The following day, the children are subjected to many threatening creatures, all of which turn out to be robotic. When the kids return to the cabin, they find Ivanna slumped over a table, and they learn that she is also robotic, with a wind-up key in her back.
Luka enters the cabin, removes his fake hair, and reveals that he created Ivanna, the Fantasy Forest, and all of the creatures within it. Luka's family uses these creations to protect their treasure from thieves. Since Justin and Marissa survived the test, they are awarded the silver box that Ivanna alluded to earlier. They leave the cabin and find their father. The trio learns that the box contains an egg, not the Lost Legend. They go to Luka, and he explains that the Lost Legend belongs to nomadic group in the woods.
Luka directs the trio to the group, and Mr. Clarke asks the nomads for the Lost Legend, and they give it to him and leave. The first words of the document say, "WHOEVER OWNS THE LOST LEGEND WILL BE LOST FOREVER." Suddenly, Mr. Clarke realizes that he doesn't know where they are.
Justin wants to help others, especially his father, but he is incredibly clumsy.
Marissa is obstinate and tends to complain, but she is also curious and fairly loyal to Justin.
During the story that their father tells, Justin is characterized as "big and athletic", and Marissa is characterized as "tiny and skinny". Marissa is described as having red hair, blue eyes, and freckles.