The Name of This Book Is Secret is the first book in the Secret Series. It is based on smell.
When Gloria Fortune, a real estate agent for the dead, finds a mysterious box in a magician's house called The Symphony of Smells, she brings it to Cass's grandfathers. When Cass and Max-Ernest go back to the house, they find a secret room and Gloria comes down with newlyweds that are looking for a house. After putting together the secret to the Symphony of Smells, Benjamin Blake is kidnapped. After initially loathing him, Cass decides it's her job to save him. However, during this time, Cass and Max-Ernest stop being collaborators because Max-Ernest thinks it's too dangerous and Cass decides to leave on her own.
After leafing through some Minight Sun Spa brochures collected by her mother, Cass decides to pose as one of the Skelton Sisters, a teen pop sensation, and calls The Midnight Sun spa to pick her up in a limousine. When it arrives she meets a very tall woman named Daisy. She tells Cass that she knows who she is and the driver drops them off. The Midnight Sun spa is said to be a pyramid with a "gleaming orb of light at the summit".While being guided to her luxurious suite, she spots Gloria in a younger appearence lounging out at the pool. Gloria is unaware and distracted to the truth and is taking pleasure of her stay.Cass then meets Owen, a stammering attendant who sets up her room and tries to please her. Cass finds Owen the most appealing out of all those at the spa.Ms. Mauvais and Dr. L catch Max-Ernest and Cass and tell them they are trying to find out what the Secret is and try to get Cass and Max-Ernest to tell what the Secret is. Cass and Max-Ernest are (understandably) confused about why they were the ones asked about the Secret.Later that night Owen comes into Cass's room, speaking with a unfamiliar accent (surfer) and no stutter, a notable characteristic he had when she last met him. Max-Ernest and Cass rejoined as Owen leaves to get a limousine and get them all away. The two discover that the goal of the Midnight Sun is to achieve everlasting life (that's what the Secret is, the formula for immortality.) They save Benjamin and a fire breaks out, but before it is implied that Ms. Mauvais' conspirator Dr. L is Pietro Bergamo's twin brother, Luciano.Owen meets up with Max-Ernest, Cass, and Benjamin and they all flee away from the spa in the limousine as the light from the orb atop the pyramid dims and eventually goes out. On the way home the limo crashes into a truck, inside the car was Grandpa Larry and his dog looking for Cass.Owen sets off on his own in the limo while Benjamin, Cass and Max-Ernest drive home with Grandpa Larry. Cass and Max-Ernest become collaborators again shortly before the end. Just a month after this experience, Max-Ernest and Cass find a hidden message inviting them to become a part of the Terces Society. Cass and Max-Ernest are each given things from P.B, (Pietro Bergamo) a super backpack and a de-coder respectively.