Denny is the reader's younger brother, so they're held responsible for him. While exploring the Museum of Natural History, Denny finds a time traveling device, invented by a man named Dr. Peebles. Denny is transported through time, and the reader is tasked with tracking him down; they are informed that he will "disappear into timelessness" if he isn't brought back within two hours.
Denny's fate changes based on the reader's decisions. In one ending, the reader and Denny end up in the Corridors of Time, and Denny is seen as an old man. In another ending, the reader and Denny fall into quicksand, presumably dying. In yet another ending, Denny becomes a prince in medieval times. There are endings where Denny is rescued, and the reader's life goes back to normal.
Denny is troublesome. Throughout most storylines, he shows very little respect for the reader. He continuously whines and complains. Denny is rebellious, and he repeatedly shouts, "You’re not the boss of me," at the reader.
Denny is described as being smaller than the reader and having red hair.
- Denny says, "You’re not the boss of me," fourteen times throughout the entire book.