The Green Sheep — Diana Kimpton

When a green sheep suddenly appears in the next-door field, Tom is amazed to discover that it's really an alien in a not-very-good disguise. Being green is only one of the sheep's problems. It also bleats backwards and duplicates itself every time it goes to sleep. Worse still, it's being hunted by a mysterious government organisation that experiments on aliens and Tom's dad is one of the hunters. With the aliens multiplying and his dad closing in, can Tom help the sheep escape from Earth before it's too late?
Shortlisted for the Rubery Book Awards 2015
A fast moving and riotously funny story (Rubery Book Award judges)