A thrilling new Doctor Who adventure, by one of the world's most renowned science fiction writers! Adjacent to our universe lies another slice of reality, with its own galaxies, stars and worlds. The two have been separate since the dawn of time, never touching, never meeting. Until the Sild broke through into our universe. Now they wait, sleeping in stasis on board their war fleet, but ready to continue with their invasion. UNIT is brought in to investigate a series of shipping losses and attacks on drilling platforms. The Doctor believes that it is the work of a previously unknown marine intelligence. What he doesn't know is the true target of these attacks. But the Doctor and Jo have other problems. Soon the Doctor will have to act to protect his old adversary - the Master. No matter how much this conflicts with his basic sense of right and wrong, the Doctor knows that all life on Earth now depends on whether the Doctor can save his nemesis for the Sild are waking.