This is an example of Terrance Dicks at his best writing. No vanilla narrative here. The Daleks have invaded Earth in the future and a team of rebels have discovered a way to travel back to the twentieth century, Their mission is to kill Sir Edward Styles, the one man upon whom the peace of the world rests. The rebels' history paints a different story, that Styles was the cause of a massive world war that made Earth easy pickings for the Daleks, The Doctor travels to the twenty-second century initially to save Jo who got transported there by accident. Upon being freed of a Dalek prison by the rebels, he learns of their mistake. It was they who caused the peace conference to fail and plunge the world into the chaos that exists in the twenty-second century. There's not much downtime in this book and Dicks gives some character moments, something his more vanilla writings don't take time to do. This is a great adventure for the 3rd Doctor, Jo, and UNIT and allows the Doctor to time travel without the TARDIS during his exile to Earth. Highly recommended.