Marty the Cat is first mentioned in the first book. Marty is Sophie's cat, and it is shown that Sophie cares deeply about her beloved pet. In addition, when Sophie is about to leave with Fitz to her "own" world, she hugs Marty, and assures her cat that her little sister Amy will take care of him. She didn't want to leave him behind, but she knew she had to.It can be noted that Marty has gray fluffy fur. In the fourth book, Mr. Forkle mentions that he knows Sophie found Marty in a bush, and begged her parents to let her keep him. Sophie reminisces about Marty's crackly purr when listening to Iggy. In Nightfall, when Sophie, Keefe, and Fitz rescue Amy, she (Amy) begs to bring Marty and Watson with them. Alden later shows Sophie his shredded sleeves, from taking Marty and Watson down the whirlpool to Atlantis. Luckily, they were okay.