The grandson of the infamous Dr Jekyll returns to London from Ceylon in the 1930s when he receives an inheritance. As he delves into his family's mysterious past, he does not realise he is being pursued by members of a secret society - while a ruthless spymaster intends to use him as bait for a trap.

Robert survives an attempt on his life, but is not sure how. He follows the advice given to him by Lily and Max, and goes looking for answers in his grandfather's house. His search leads him back to the East End, where he was attacked, and an unexpected encounter at the Empire Hall. Meanwhile, Ravi has to face both the colonial police and the undead to bring Robert urgent news from Ceylon.

Robert becomes determined to rid himself of his alter ego, and as he falls in love with Lily, he resolves to keep Hyde a secret from her. In desperation, he takes some of the potions he finds in his grandfather's laboratory. Garson tells Robert that his grandmother may still be alive, and he sets off in search of her - but Captain Dance is also trying to track her down.

Wracked with guilt after failing to get to his grandmother Maggie before Captain Dance's men, Robert, Lily and Garson work tirelessly to cure her of sepsis. Garson makes the chance discovery that Hyde's blood has antibiotic properties. Dance and Bulstrode play cat and mouse in their pursuit of Hyde because Dance believes that only Hyde can help him resurrect the demonic Lord Trash. Robert risks everything by turning into Hyde, but will he be able to save Maggie?

Robert discovers he has some distant relations, so he and Max travel to the remote village where they live in the hope they will be able to tell him more about the Jekyll curse. On their arrival, they discover several mysterious deaths have occurred recently and the locals believe a legendary demonic dog is responsible. Robert discovers an ancient book that seems to reveal a connection between his relatives and Tenebrae, and suspects they are dealing with a shape-shifter.