Olly Brown, God of Hamsters by Bethany Walker

Olly Brown never gets to take home the Year 6 class hamster because his overprotective dad has some weird hang-up about how much responsibility pets are and how sad it is if/when hamsters die.
 
But then the most amazing thing happens: a hamster shows up in Olly's house anyway and it can communicate with him! This new hamster, Tibbles, is in awe of Olly, and it turns out, Tibbles is not alone: there's a whole civilisation of super-advanced, intelligent hamsters who seem to be worshipping Olly as a god?! This is so awesome!