In the fifth book of the Calendar Mysteries—a new early chapter book mystery series featuring the younger siblings of the A to Z Mysteries detectives—twins Bradley and Brian Pinto are getting ready to celebrate Mother's Day by treating their mom to a show by Hypo, the world's greatest hypnotist. Brian hopes that if Hypo can hypnotize his mom into loving ducks, then she will let him raise ducks in their backyard. But when the Pinto family gets home from the show, the twins' mom starts acting strange. She splashes in the bathtub for hours, she leaves corn kernels all over, and—could it be?—she quacks! Bradley thinks his mom has actually turned into a duck! How did this happen? Can Bradley and Brian, with help from their friends Lucy and Nate, turn their mom back into their mom?