Jumping the Scratch by Sarah Weeks

Jamie Reardon has always heard that bad things come in threes. So after his cat, Mister, dies, his father leaves, and his aunt Sapphy has an accident that causes her memory to develop a skip, Jamie hopes his life will go back to being as normal as cornflakes. But unfortunately there's one more bad thing in store for Jamie—something he'd give anything to be able to forget—and this one leaves him feeling like a stranger to himself. Jamie tries in vain to find the magic trigger that will help Sapphy's memory jump the scratch, but in the end it's Aunt Sapphy who, along with a curious girl named Audrey Krouch, helps Jamie unravel the mysteries of memory and jump the scratch in his own life.