A secret portal has lain dormant for many years, waiting for the right moment to become active. And now, that moment has arrived.

Ten-year-old Timmy Buffet and his faithful terrier Sammy find an old-fashioned red phone box in their family garden in the south of England, unaware that it possesses the power to whisk them to another time and place. Confused and disorientated after an unexpected journey back through the centuries, they stumble upon the Saxon settlement of Fingle, where they are offered hospitality by none other than the King.

As the weeks pass, Timmy becomes firm friends with King Zeva and his charismatic sister, Princess Millie, learning to ride a horse and fire an arrow, while passing on skills from the future. But all the time, he and his companions face the constant threat of attack from the Vikings, merciless invaders from the east.

After a series of strange calls to the phone box, Millie finally works out the code to take Timmy back home, but his departure is overshadowed by tragedy. And when he and Sammy surge forward to their own time, an uninvited stowaway travels with them...