You're right-Macram Owls & Encores is the prelude collection, while Rescue at Pelegon's Retreat is Book One, the first full-length novel. Here is the corrected description:
Pegasus has a business to run, a reputation to protect, and absolutely no room in his schedule for another impossible rescue.
His friends, unfortunately, have never respected his schedule.
When Wally-the Minotaur beneath the palace-overhears a secret that threatens hundreds of innocent lives, he calls upon the only companions strange enough to help: Medusa, a formidable artist who travels through mirrors; Cy, a gentle Cyclops with an unfortunate relationship with sea travel; and Gus, the legendary winged horse whose divine connections are nearly as impressive as he insists they are.
Their journey will carry them across the Aegean, through hidden cities, celestial bureaucracy, and several forms of transportation no sensible creature would willingly choose.
The gods could help.
The gods are busy.
Warm, witty, and filled with mythological mischief, Rescue at Pelegon's Retreat is a found-family fantasy about courage, loyalty, and the possibility that history remembered the monsters entirely wrong.
Book One of the Monsters, Maybe series by Wilson H. Bard.
The adventure begins in the prelude collection, Macram Owls & Encores, but readers may also begin here.
Available wherever ebooks are sold and audiobooks are heard.