Gladiola is a dog. Specifically, he is a pink miniature poodle. Sometime before the events of this story, Gladiola ran away from his wealthy family. The family desperately wants their unique dog returned and offer a two-hundred-dollar reward for him. In chapter 12, after encountering Gladiola while camped in the woods, Grover and the dog strike up an immediate rapport due to Grover's ability as a satyr to speak to animals. When he is first introduced to the poodle, Percy is skeptical. He refuses to say hello to Gladiola because he thinks the others are playing a practical joke on him.

Despite his aversion to his former pampered life, Gladiola agrees to be returned in order to help his new friends. Percy, Annabeth, and Grover need money to buy train tickets to go west to Los Angeles. However, the trio has no money to buy the tickets. Ever the helpful dog, Gladiola agrees to be returned to his family so that they can receive the reward and use that to buy their train fare. Gladiola even knows the train schedule. He tells Grover that there is a nearby Amtrak station and a train is leaving at noon. With this money, Annabeth, Percy, and Grover are able to travel as far as Denver.