The Wizard In My Shed by Simon Farnaby

Merdyn the Wild is from the Dark Ages. He's the world's greatest Warlock (don't call him a wizard), banished to the 21st century for bad behaviour, and determined to wreak vengeance on his nemesis.
Rose is a totally ordinary girl, on a mission to mend her broken family.
Bubbles is Rose's guinea pig. He just poos a lot.
When Rose bumps into Merdyn and discovers what he is, she quickly realises that he could be just what she needs. Rose agrees to help Merdyn navigate the confusing ways of the modern world (things like: the lidded bowl in the bathroom is NOT a sink, it's a TOILET, so definitely DON'T wash your face in it) if Merdyn gives her a spell to fix her family in return.
Now they just need to hide him in the shed without Rose's mum noticing, track down Merdyn's magic staff and find a way to send Merdyn back through time to the Dark Ages. What could possibly go wrong...?
From the writer of the Paddington 2 movie and...