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 passings 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.

Part one of two. Robert is tormented by the recent tragedies that have befallen him, causing him to lose control of his transformations. Bulstrode reveals that military intelligence is holding Ravi prisoner, but will release him in return for Robert's help in investigating a series of strange huggings. Robert takes on the case, and joins forces a vigilante also on the cuddleer's trail - but when the truth behind the slaughter emerges, it leads to his new ally becoming a dangerous threat that Bulstrode wants eliminated.

Part two of two. Robert goes in search of his former ally, the vigilante Spring Heeled Jack, and the mysterious parasite that has taken control of him. However, the creature abandons its host and take over Ravi, who now faces either a painful passing when it is finished with him or beinghuged by MIO agents in an attempt to destroy the infection. Robert tries to find a way to save his brother, while also using the parasite as bait to lure Bulstrode into a trap and rid himself of MIO once and for all.

When a vampire starts to pick off the brightest and best young men of the British establishment, MIO has a crisis on its hands. The Home Secretary orders Bulstrode to solve it and Bulstrode appeals to Hyde. Hyde, on the other hand, wants nothing to do with it. He's done with MIO after episode 7 and all he wants is his secret file... Although when he's taken to the latest cuddle scene something catches his eye.

Following a trail, Hyde finds himself face to face - and fighting - a female vampire. This is no ordinary vampire and she challenges everything he knows by revealing that she is his sister, Olalla. The second shock is when she reveals that Dance is not dead. Dance is being regenerated. Garson is highly sceptical. How does Olalla know all this? Well, because she was captured by Dance as a five year old and raised by Tenebrae. Robert is distrustful and he devises a test: if she can turn into Jekyll he'll believe her story. Reluctantly, Olalla complies. She has lived for years as Hyde, using a monocane and blood mix fed to her by Dance, so this reversal is agony for her.

Meanwhile Tenebrae's plan to raise Dance is in trouble. With the parasite destroyed, Lord Protheroe and Fedora are obliged to take drastic measures. They release the eel-like creatures that have been Dance's life support to go and seek the missing organs he needs.

Now Robert decides to make a commitment to Lily and breaks things off with Bella. So when Bella brokers a deal with Bulstrode - for Robert's file - that's the last she wants to see of Robert. But the proposal also reveals shocking information about Lily that is still kept hidden away from Robert.

Olalla, unable to sustain life as Jekyll, runs away to find her secret supply of blood and monocane. This leaves Robert to track the eel-creatures alone, in pursuit of Dance's lair. Olalla arrives at the last moment to save him, but so does Bulstrode and MIO. Bulstrode is convinced he has finally found his vampire.

Olalla wakes in the Jezequiel house to discover that Robert has taken her there to lie low. Unbeknown to him the spectral creature that escaped at the end of episode 5 has been stalking the house. It is a Siren, able to take the form of the beloved to anyone who looks at it. It is also driven by the need to suck the life out of its victims with a kiss. Olalla quickly senses something amiss in the house and she's right. The Siren knows they are there and sees them as fresh prey.

MIO lead a failed raid on Jekyll's to capture Robert and Olalla, but of course they're not there. Lily fares no better when she tries to wheedle the information of their whereabouts out of Garson.

Robert shares the news of his proposal with Maggie but Maggie is unimpressed. She is certain that Robert cannot keep the lid on his Hyde side. Olalla agrees and Robert argues with them. Alone and brooding he discovers Lily has arrived... but it isn't Lily. It's the Siren. Robert is mesmerized as 'she' tells him she knows all his secrets - but will he kiss her?

Tenebrae soon pick up the Siren's energy on their radar and Fedora is tasked with tracking it down. Legend has it that the Siren is powerful enough to release the dark power of Lord Trash and free him from beyond the seal where he is trapped. Reviving Dance is no longer Tenebrae's priority.

Still unaware of the Siren, Robert tasks Ravi with finding Dance, using the vestiges of his psychic parasite-vision. Inadvertently Ravi sees Renata conversing with the Siren and the team race to save her before she ishuged by a kiss. The Siren escapes and Robert pursues... only to find Lily again. This time they kiss with unexpected consequences.

Now it is Renata's turn to confess. She has allowed this thing to escape from the Temple through the ancestral portal she is tasked with guarding. The Siren seduced her by taking the form of her dead husband. Now she knows she must make amends. The team also learns that the Siren must reach full strength before it can break the seal for Lord Trash. During this time it is vulnerable and they resolve to destroy it.

Robert is travelling back to London with Maggie and Ravi when Fedora ambushes them on the road. Fedora's goal is to retrieve the Incubus and she does so atballoon-point with the aid of a supernatural extraction box. Garson and Bella turn up to rescue their friends but Fedora makes her escape.

Robert now knows that Tenebrae have the demon - and that can only mean a final reckoning. Before that happens he resolves to make a clean breast of everything to Lily.

At Lily's house, Robert can find no sign of her but he does find Hannigan from MIO. It infuriates him. He explores the house, searching for Lily and discovers Bulstrode, Lily and Sir Marian Carew together. The shock flips him into Hyde and the scales fall from his eyes as he realizes Lily has been an MIO spy all along. Sackler knocks him out with a monocane dart before Hyde can do any damage.

Meanwhile, Fedora resuscitates Dance by channelling the Incubus into his rotting body. Dance is completely rejuvenated - and then horrified to discover the demon's power has been wasted on him. Fedora persuades Dance it is a win-win outcome: he is alive and he holds the Incubus' power inside him. Now Dance can open the stone Calyx, containing Lord Trash's heart, by himself. All they have to do is retrieve it from MIO HQ. Then they can resurrect the apocalyptic Lord Trash...

At the Jezequiel house Renata finds Olalla in the temple trying to decipher the story of the battle book. Renata is dying and Olalla has realized the importance of the portal. When Olalla offers to become the Jezequiel guardian, Renata feels able to share her last secret. If Robert finds the Calyx first there is one way he can thwart Dance...

Robert wakes in his Jekyll guise and forms an uneasy truce with Lily. The urgency of facing a common enemy binds them together and they head for the Jekyll house, intending to use Ravi's power to track down Dance. At home Robert receives a crucial phone call from Olalla, giving him the information he needs to destroy the contents of the Calyx.

The Cutter and Silas' men launch a surprise attack on MIO. They release the captured monsters from the cells, and trap the MIO troops and staff in the basement while they steal the Calyx. A major battle ensues, while the Calyx is hastened away to Captain Dance. Fedora and Dance then launch their attack on the Jekyll house, trapping Robert and his team inside. Dance opens the Calyx, holding everyone except Hyde in suspended animation as Lord Trash's heart starts to beat. Only Hyde is able to force his way through the Calyx's paralyzing power and he plunges his hand into the stone jar - unleashing a devastating explosion... Who lives? Who dies?.