Wizard In My Shed

Merdyn the Wild is from the Dark Ages. Hes the worlds greatest Warlock (dont call him a wizard) banished to the 21st century for bad behaviour and hes about to create a whole load of trouble for Rose aged 12. Rose is a totally ordinary girl on a mission to mend her broken family. Bubbles is Roses 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 its a TOILET so definitely DONT 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 Roses mum noticing track down Merdyns magic staff and find a way to send Merdyn back through time to the Dark Ages. What could possibly go wrong?