''Mass Effect: Deception'' is a novel written by William C. Dietz set in the ''Franchise/MassEffect'' universe. It chronicles Gillian Grayson's attempt to avenge her father's death at the hands of Cerberus in ''Literature/MassEffectRetribution''.

The novel is the only ''Mass Effect'' book to not be written by Creator/DrewKarpyshyn and contains many continuity errors.
!!''Mass Effect: Deception'' provides examples of the following tropes:
* ArtisticLicenseBiology: You cannot outgrow autism. You can learn to control it with time. You can use drugs that help control some of the symptoms. But you cannot outgrow it.
* BuryYourGays: A previously established homosexual male character [[SuddenlySexuality is turned straight]] before he's killed off.
* ChronicBackstabbingDisorder: Kai Leng gets two mercenaries to help him steal Grayson's body. He traps one of them in a containment device to act as a decoy, prompting the other merc to demand payment up front. He complies and kills that merc a few hours later.
* CanonDiscontinuity: At least the original editions, which a rewrite will replace in the continuity.
* ContinuitySnarl: See [[https://docs.google.com/document/d/1XBpMF3ONlI308D9IGG8KICBHfWKU0sXh0ntukv-_cmo/preview?pli=1&sle=true here]]. Long story short, the novel makes ''many'' errors regarding the lore of the ''Mass Effect'' universe.
* CuttingOffTheBranches: The Citadel Council in ''Deception'' are made up of an asari, a turian, a salarian and a human. Thus, the playthrough where a Renegade Shepard sacrifices the ''Destiny Ascension'', making Udina appoint an all-human Council (as opposed to a still-mixed-species Council for a Paragon Shepard) is invalidated. ''VideoGame/MassEffect3'' later confirmed this, as there is no all-human Council in it, either, unless it abdicated between the games. Notably the human councilor is ''not'' identified as Udina despite ''Retribution'' implying otherwise, but his actions and personality identify him clearly as such. Nobody's sure why the author didn't name him.
* DefeatMeansFriendship: Despite their sole interaction being a one-sided conversation that ended with him being thrown across a room, Nick greets Gillian with open arms and a kiss on the cheek when he sees her again.
* DownerEnding: [[spoiler:Gillian, Nick, and Hendel all [[DroppedABridgeOnHim die pointless deaths]], Kai Leng gets away again, the Illusive Man is building an ''army'' of Grayson clones (or something possibly ''worse'') and once again the Council sticks their heads in the sand and ignores Kahlee and Anderson's evidence about the Reapers.]]
* DroppedABridgeOnHim: [[spoiler:Gillian, Nick, and Hendel.]]
* EnemyEatsYourLunch: Kei Lang eats Anderson's cereal while planting a bug in the latter's house.
* EvilIsPetty: As noted above, Kai Leng eats Anderson's cereal.
* KarmaHoudini: [[spoiler:Kai Leng, natch. Gotta keep him alive for ''Mass Effect 3'', after all. Don't worry, Shepard will [[ImpaledWithExtremePrejudice give him what's coming to him]].]]
* IdiotBall:
** After already losing Nick on the Citadel, Kahlee decides it would be a good idea to let an emotionally unstable Gillian go outside for a spot of fresh air after she's announced her intentions to kill the Illusive Man. Three seconds later she's missing too. The novel does point out this was incredibly stupid thinking on Kahlee's part.
** Aria T'Loak uses next to none of the security she used in previous books/the second game. Luckily for her, Kai Leng has forgotten about the advanced tactics he used in previous novels as well.
* IGaveMyWord: After one of Aria's banks is hit by the Grim Skulls, she lets one of their captured mercenaries go after the merc tells Aria who really killed her daughter. When Aria later confronts the same merc in the Grim Skulls' medical bay, she has her transferred to a hospital, her reason being this.
* ImprobableWeaponUser: Kai Leng [[spoiler:kills Gillian with a sharpened toothbrush]].
* IndyPloy: This is Gillian's modus operandi for the entire novel. [[spoiler:And it very nearly works out.]]
* NotSoStoic: Aria breaks down in tears over her daughter's grave at Thessia, despite her best attempts not to do so.
* SlowlySlippingIntoEvil: Gillian and Nick. Hendel does as well to a lesser extent. [[spoiler:And they all die for it.]]
* ThatMakesMeFeelAngry: A great deal of criticism has been focused upon the author's inability to write characters in a natural manner.
* TheMole: [[spoiler:Cory Kim, ex-partner to Kai Leng, is a deep undercover Ceberus operator in the Biotic Underground. Her cover story is that she quit Cerberus before joining up with the Underground, which even Kai Leng believed at first.]]
* ThrowingOffTheDisability: Gillian has completely lost her autistic behavior by the beginning of the novel.
* TookALevelInBadass: Gillian and Nick have both taken great strides during their teenage years. Too bad the strides were down a slippery slope.
* WellIntentionedExtremist: The Biotic Underground claim to be this, but it's clear they're just vying for power.
* WoobieDestroyerOfWorlds: Gillian, who goes on a quest to avenge her father's death.
* YouKilledMyFather: Gillian toward the Illusive Man, but there's a few more variations of this as well; [[spoiler:Aria to Kai Leng over her daughter, Kai Leng to Gillian over his ex-lover, and Nick to Hendel over his girlfriend.]]
* YourHeadASplode: [[spoiler:Cory Kim's fate, courtesy of a {{hand cannon}} wielded by Gillian.]]