A struggling musician named Hector P. Valenti discovers a crocodile with a unique talent for singing, which he deems his ticket to stardom. He names the crocodile Lyle and brings him to New York City, aiming to introduce him on the big stage. Unfortunately, Hector's plans don't work out as expected, and he leaves Lyle hidden in an attic of a brownstone in the city. The brownstone soon becomes home to the Primm family, who have just moved to the area. While adapting to their new life, young Josh Primm discovers Lyle upstairs and is initially frightened by the singing reptile. Beginnings are difficult, but as they overcome their initial fears, Josh and Lyle form a secret friendship.

As Lyle and Josh grow closer, his parents, Mr. and Mrs. Primm, remain unaware of the crocodile living in their home. However, their neighbor, Mr. Grumps, and his cat, Loretta, hold suspicions about strange noises coming from the building. Lyle's presence eventually poses a threat to the peace and anonymity he enjoys, sparking tension in the community. The story explores themes of acceptance, friendship, and the clash between pursuing one's dreams and the complications that arise when those dreams involve the unconventional presence of a singing crocodile in a big city.