Long Hot Summoning — Tanya Huff

IT STARTED ON THE LAST DAY OF HIGH SCHOOL...
a day Diana Hansen had been anticipating for the last twelve years. Now her real life could begin.... For Diana, like her sister Claire, was a Keeper--gifted with the ability to reweave the possibilities of time and space to maintain the balance between Light and Darkness. What neither Diana nor Sam--formerly an angel, now a cat--could have anticipated was that her first Summons as an active Keeper would be to a shopping mall!

But a quick trip to the Erlking's Emporium, a gift shop in a Kingston mall, confirmed Diana's worst suspicions. Not only was Darkness trying to stage a takeover from the Otherside, but if Diana didn't bring in reinforcements, her first Summons might well be her last. Claire and Austin--who'd always been a cat and had little tolerance for cat wanna-bes like Sam--were only too ready to take on the "older and wiser" roles. But neither the Keepers nor their cats were prepared for what they found when they tried to cross from their world to the Otherside mall....