The Blythes are a big, warm, rambunctious family who live on a small farm and sometimes foster children. Now Prez has come to live with them. But, though he seems cheerful and helpful, he never says a word.

Then one day Prez answers the door to someone claiming to be his relative. This small, loud stranger carries a backpack, walks with a swagger and goes by the name of Sputnik.

As Prez dithers on the doorstep, Sputnik strolls right past him and introduces himself to everyone in the household. Prez is amazed at the response. The family pat Sputnik on the head, call him a good boy and drop food into his mouth. It seems they all think Sputnik is a dog. It's only Prez who thinks otherwise.

But Prez soon finds himself having to defend the family from the chaos and danger unleashed by Sputnik, as household items come to life - like a TV remote that fast-forwards people: 'Anyone can do it, it's just that people don't read the instructions properly'; and a toy lightsaber that entertains guests at a children's party, until one of them is nearly decapitated by it - and Prez is going to have to use his voice to explain himself.

It turns out that Sputnik is writing a guidebook to Earth called Ten Things Worth Doing on Earth, and he takes Prez on a journey to discover just those 10 things. Each adventure seems to take Prez nearer to the heart of the family he is being fostered by. But they also take him closer to the day that he is due to leave them forever....