This collection of excerpts from the novel Deep Blue follows the Doctor and his companions, Tegan and Turlough, as they investigate a horrific alien threat in the coastal town of Tayborough Sands. The narrative begins with a fishing crew hauling in mutated sea life that violently attacks them, triggering a water-borne infection that transforms humans into spike-covered, aggressive Xaranti hybrids. UNIT, led by the Brigadier and Captain Mike Yates, struggles to contain the escalating chaos as the local population succumbs to a hive-minded bloodlust. The tension peaks as a Morok battle cruiser lands on the beach, revealing the true scale of the extraterrestrial invasion. Throughout the story, the characters face personal and physical crises, culminating in the Doctor's telepathic and scientific efforts to reverse the transformation and repel the Xaranti queen.