Mortal Coil recap

Sensitives, the sorcerers who see the future, are being murdered one after another, and every one of them had seen the same vision: a sorcerer called Darquesse destroying the world. While Skulduggery and Valkyrie investigate, a far more immediate threat gets loose, as thousands of Remnants, parasitic creatures that possess a host and unlock the worst of them, escape and sweep through Ireland, taking the Sanctuary and much of Dublin with them. Kenspeckle Grouse is killed in the outbreak. Valkyrie then learns what the visions meant: her true name is Darquesse. Speaking a true name unlocks everything a sorcerer can be, and when there is no other way to stop what is happening, Valkyrie becomes Darquesse, a being of enormous power and no restraint who fights the returned Lord Vile to a standstill before Valkyrie is brought back to herself. The Remnants are contained. Valkyrie has her true name sealed away so Darquesse cannot surface again, and Skulduggery helps her hide it. In the last moments, a Remnant takes Tanith Low, and the possessed Tanith escapes.

Previously: Stephanie Edgley became Valkyrie Cain, partner to the skeleton detective Skulduggery Pleasant in a hidden world of sorcerers. She killed Nefarian Serpine with the Sceptre of the Ancients, stopped Baron Vengeous from waking the Grotesquery, and learned that she is descended from the last of the Ancients. When the Diablerie opened a portal at Aranmore Farm, a Faceless One came through and killed the Sanctuary's Elders and Mr Bliss, and Skulduggery drove it back through the portal and was trapped in the dark gods' dead world. Valkyrie spent months getting him out, crossing over at last with the Teleporter Fletcher Renn and the Dead Men, Skulduggery's unit from the war. In the same case, Thurid Guild was removed as Grand Mage and replaced by Erskine Ravel, with Ghastly Bespoke and Madame Mist as Elders, and the armour of Lord Vile, a Necromancer general missing since the war, reappeared with an unknown wearer inside it who killed the Torment. Valkyrie has been training in Necromancy with Solomon Wreath, whose order is waiting for a figure of prophecy called the Death Bringer.

Sensitives, the sorcerers who see fragments of the future, are being killed. They are not a dangerous or a powerful group, which makes the murders difficult to explain, and Skulduggery and Valkyrie start work with no motive and a shrinking list of witnesses. Valkyrie is fifteen now, competent, busy, and living almost entirely on the magical side of her life while a duplicate handles school and her parents. Her Necromancy training with Solomon Wreath continues, to Skulduggery's steady disapproval, and the Sanctuary under Erskine Ravel is friendly enough to let them work without interference.

The reason for the killings turns out to be what the Sensitives have been seeing. All of them, independently, have had the same vision: a sorcerer called Darquesse, of overwhelming power, destroying the world and enjoying it. Nobody knows who Darquesse is or when it happens, and the people who have looked hardest at the vision have not survived long afterwards. Finbar Wrong and Cassandra Pharos, both Sensitives and both still alive, confirm the shape of it. It is not a warning that can be acted on, only one that can be feared, and it is now the most closely held secret in the magical world.

The investigation runs into a second and far more immediate danger: the Remnants. They are creatures without bodies of their own, thousands of them, kept sealed away for generations because a Remnant that reaches a person takes them over completely, wearing their face and their memories while removing every restraint they ever had. The victim is still in there and is no longer in charge. The seals do not hold. What begins as a handful of possessions becomes an outbreak, and the people it takes are people Valkyrie knows.

The Remnants sweep through Dublin and into the Sanctuary itself, and the institutions that are supposed to handle a crisis of this size are among the first things lost. Skulduggery, Valkyrie, Ghastly, Tanith and Ravel are reduced to a small group of people who can still be trusted to be themselves, fighting former colleagues who cannot be killed without killing the host. Kenspeckle Grouse is killed during the outbreak, leaving Clarabelle alone in the facility behind the cinema. There is no reinforcement coming and no obvious way to put thousands of Remnants back where they came from.

Valkyrie learns what the visions were about. Every sorcerer has a true name, the word that is what they actually are, and speaking it unlocks the whole of their potential and hands anyone who knows it total power over them. Hers is Darquesse. The being who burns the world in every Sensitive's vision is not a stranger to be hunted down and stopped in advance; it is her, waiting inside her name. Skulduggery, who has reasons of his own for understanding what a person can become, keeps it quiet rather than handing it to the Sanctuary, and Valkyrie has to decide what to do with a truth she cannot give back.

With the Remnants winning and nothing left that works, Valkyrie's true name is unlocked and Darquesse takes over. She is immensely, casually powerful, indifferent to everyone she was fond of an hour earlier, and delighted with herself. Lord Vile comes for her, and the two of them fight without either being able to finish it, the first time anyone has seen what is in the armour tested at that level. Valkyrie is eventually brought back to herself, with the memory of everything Darquesse did and, worse, of how much she enjoyed being her.

The Remnants are driven back and sealed away again, at a cost the Sanctuary spends years counting. Kenspeckle Grouse is dead. Valkyrie, unwilling to risk Darquesse ever surfacing again, has her true name sealed so that it cannot be spoken or used, by her or by anyone else, and Skulduggery helps her keep the whole business off the record. It should be finished. Then, as the last of the outbreak is being cleared up, a Remnant takes Tanith Low. The possessed Tanith walks out with her own face, her own skill with a sword and none of her own loyalties, and disappears, leaving Valkyrie without her closest friend and the world with a very capable new enemy who is certain that Darquesse is coming. Lord Vile's identity remains unknown.

The Remnants are driven back and contained, but the case ends with the ground moved under everyone. Kenspeckle Grouse is dead, killed during the outbreak, and Clarabelle is left running his facility without him. Valkyrie knows what the Sensitives were seeing: Darquesse is her true name, and the sorcerer who burns the world in every vision is her. She has been Darquesse once, briefly and completely, long enough to know how much she enjoyed it and how little of Valkyrie was left while it lasted, and long enough to have fought the thing in Lord Vile's armour to a standstill in front of witnesses. To make sure it cannot happen again, she has her true name sealed away, which should put Darquesse permanently out of reach. Skulduggery keeps the secret with her rather than reporting it. The worst blow is Tanith Low: as the Remnants are being rounded up, one takes her, and the possessed Tanith escapes with her own face, her own skill and none of her own loyalties. She is now somewhere in the world, on the other side, and she believes in Darquesse. Lord Vile's identity is still unexplained.