The Secret Country by Jane Johnson
Ben has been saving for weeks to buy the Mongolian fighting fish he's seen in the local pet shop. But on entering Mr Dodds' Pet Emporium, a small cat hooks his claws into Ben's jumper and begs to be bought. The cat tells Ben that Mr Dodds is importing rare magical beasts into this world and he needs his help to save them. Like fish out of water, they are dying in this world, away from their magical land. A parallel world, Eidolon, exists as a neighbour to our own and is filled with magic and magical creatures, like dragons, selkies, sabre-toothed tigers and faeries. With his new friend, Iggy the talking cat, Ben travels between the worlds and helps some of these amazing creatures return home. On his journey he makes loyal friends, encounters danger and adventure and discovers his own royal lineage in the Secret Country.