When Hamish and Suzy Hamilton relocate to the Cornish town of Warfield with their parents to start a new life, they discover an ancient stone circle built under their home. The only point in the entire universe where chaos and order are always balanced, Equilibrium is also a gateway through which brother and sister must travel to 1597 to restore harmony and save the world from catastrophe. Armed with only a dagger each and a curious timepiece, Hamish and Suzy embark on a rollercoaster journey through Tudor England, becoming embroiled in plots and rebellion that will bring them face to face with Queen Elizabeth I herself. Meanwhile, England stands on the brink of invasion and in a race against time Hamish and Suzy must repel the Spanish Armada and avert a calamitous change to the course of history. But whether they can succeed and whether they can return home alive are different matters entirely …