Light Thickens is a 1982 detective novel by Ngaio Marsh, and her final work featuring Superintendent Roderick Alleyn.
The story is set in London, and centred on a theatre production of Macbeth. The first half of the novel delves in great detail into the process of rehearsing and preparing the production, and fleshes out the characters, including the director Peregrine Jay and his wife and sons, the distinguished leading man Sir Dougal Macdougal (who plays Macbeth), the gracious and reserved leading lady Margaret "Maggie" Mannering (Lady Macbeth), tall, dark Simon Morten (Macduff), superstitious and fearful Nina Gaythorne (Lady Macduff), beautiful-voiced communist sympathiser Bruce Barrabell (Banquo), the young Maori man Rangi who plays one of the three witches alongside two girls, the highly eccentric and formidable weapons master Gaston Sears, and child actor William Smith whose family history holds a dark secret. Both Sir Dougal and Simon are attracted to Maggie, who insists she does not become attached during the preparations for the production; meanwhile, the two men are fiercely trained for the final fight of the play by Gaston, who insists that they wield very heavy replicas of the authentic weapons.
After some of the actors inevitably begin to talk of the superstitions surrounding the play, menacing omens from Macbeth begin creeping out into real life: Peregrine is bruised by the handle of a misplaced claymore, Simon and Dougal are unnerved by appearances of Banquo's dummy heads in an offstage room and under a prop serving dish on the stage, and Rangi discovers half of a killed rat in his prop bag while rehearsing; Peregrine assumes that one of the cast or crew is a malicious prankster and forbids any further talk of the incidents.
The production is an unbelievable success and earns rave reviews. Two weeks in, Peregrine brings his family to see the play, and Superintendent Roderick Alleyn is also in the audience. In the final scene, it is not a dummy head that is brought onto the stage on the end of a pole...
The story contains examples of:
- All Part of the Show: For the benefit of the audience, the murder has to be covered up this way. It is mentioned later that those of the audience who noticed just thought that the head was an "awfully good dummy".The blood drips onto Seyton’s upturned face. And being well-trained professional actors, they respond, with stricken faces and shaking lips, "Hail, King of Scotland!" The curtain falls.
- Black Mage: Gaston Sears is believed by some to be one.
- Busman's Holiday: Superintendent Alleyn is in the audience watching the play when the murder occurs.
- Clock Discrepancy: Alleyn initially tries to make sense of the fact that after Macbeth's final exit fighting Macduff, the murder of Sir Dougal and the switching of his head for the dummy head on the claymore only had three minutes to take place. Actually, during Macbeth's final scene, he was played by Gaston, who had already committed the murder before.
- Crystal-Ball Scheduling: Macbeth's hallucinations and his bloody murders come to frightening life for the theatre cast, who are shaken by the unexpected appearances of severed heads on the stage during their rehearsals, and ultimately by the decapitation of Sir Dougal.
- In the theatre production, the apparitions of Banquo's ancestors, depicted by crafted dummy heads, unnerves Macbeth. During the course of Light Thickens, the heads are planted in various places to shock and unnerve the actors during rehearsal, by the actor of Banquo, Bruce Barrabell.
- Dead Person Impersonation: Gaston does this for Macbeth's final scene, having killed Sir Dougal, in order to give the impression that he is still alive and acting.
- Decapitation Presentation: During the final scene in one of the performances of Macbeth, the prop head brought in on the end of a claymore is replaced with the real head of Sir Dougal, who plays Macbeth.
- Evil Weapon: Played with. The deranged and wildly imaginative Gaston Sears believes the claymore to be associated with decapitation, and allows this to take control of him.
- Foreshadowing: Loads of it in the first half of the novel, especially in the unnerving appearances of dummy heads during rehearsal.
- Gone Horribly Wrong: Barrabell's plan to have William Smith sacked by framing him as a prankster not only fails, but ends up unnerving the entire cast and crew, and is implied to have indirectly stirred the murderer's wild imagination.
- Graceful Loser: The killer, Gaston, tells the police he was expecting them, and calmly and politely confesses the whole crime to them, only asking that they take care not to lose the letters in his possession. His final letter to William, accompanying his gifts, even reads "Regrettably, I shall not be at liberty to teach you but Mr. Simon Morten will, no doubt, be glad to do so..."
- Innocent Prodigy: William Smith. Even though he's the son of a criminally insane killer.
- Irony: During the reconstruction of the crime, of necessity, Gaston Sears had to pretend to be Sir Dougal during the replay of the last scene. It turned out that he actually impersonated Sir Dougal during the fatal performance, having killed the other actor beforehand.
- Kill and Replace: Gaston kills Sir Dougal during the course of the final act on the fatal night, and then impersonates him as the actor of Macbeth during his final scene.
- Literary Allusion Title: The title of the novel comes from Act 3, Scene 2 of Macbeth: "Light thickens, and the crow / makes wing to th' rooky wood."
- Not-So-Fake Prop Weapon: A variation. The fake severed head of Macbeth is replaced on the claymore by the head of the decapitated murder victim, Sir Dougal.
- Revenge by Proxy: Barrabell tries to inflict a downplayed version on William Smith, whose father was responsible for killing Barrabell's wife. Barrabell's manner of revenge is to play childish and unnerving pranks on set, hoping they will be pinned on William and get him fired.
- Start to Corpse: An unusually long one. The killing only takes place two thirds of the way through the novel.
- Tall, Dark, and Handsome: Simon Morten fits this trope quite well.
- Training from Hell: Gaston puts Sir Dougal and Simon Morten through gruelling training sessions with heavy weapons to prepare for their meticulously choreographed fight scene.
- Unwitting Instigator of Doom: Bruce Barrabell; it is implied that but for his malicious pranks the murder would not have taken place.
- Wham Line: Peregrine hears his son Robin saying into the phone:Robin Jay: I forgot to mention that I knew all along the fighter wasn't Macbeth. I'll give you three guesses who...
- Wise Beyond Their Years: Peregrine's elder son Crispin. Robin and William also have shades of this.
