* CompleteMonster: While a very comedic and funny series, there are still some [[VileVillainSaccharineShow monstrous and serious villains]] to contrast:
** ''South by Southeast'': The assassin [[PsychoForHire Charon]], in truth [[spoiler:Tim Diamond's girlfriend Charlotte Van Dam]], is a deadly killer hired to kill an [[UsefulNotes/SecretIntelligenceService MI6]] Russian DoubleAgent named Kusenov as a statement, as her employers know the hit is impossible. Instead, Charon lures Kusenov to England, killing several in the way before murdering an [=MI6=] agent with ice skates. Charon rigs a bomb in an auction house where Kusenov wishes to buy a painting, intending to kill everyone in the room. Having been thwarted, Charon decides to spitefully murder Tim and his little brother Nick before establishing a permanent group of assassins to continue to profit from death and murder.
** ''I Know What You Did Last Wednesday'': [[ThemeSerialKiller The killer]] is [[spoiler:Johnny Nadler, a [[EvilFormerFriend former school friend]] of Tim's]] and a [[EvilIsPetty bitter loser]] who, following ten years after graduation of [[AlwaysSecondBest always coming in second]], irrationally blames their former friends for their own failures and thus decided to murder them all. The killer starts off by murdering their [[spoiler:best friend Rory [=McDougle=]]] by cutting him into multiple pieces, then lures the other seven to [[TenLittleMurderVictims Rory's private island, which they had rigged with remote control traps, and began picking them off]] using methods that represented the school subject they had surpassed the killer in methods including poison, impaling and being crushed to death. Upon failing to make their final intended victim, Tim, fall to his death upon the jagged sea needles, the killer confronts Tim and Nick at gunpoint and admitted to have enjoyed their killing spree, before trying to murder them both.
* WhatDoYouMeanItsForKids: Despite being comedic children's stories, the books make absolutely no bones about the nature of the various criminals the brothers face, ie dangerous killers with no qualms about [[WouldHurtAChild hurting children.]] The police aren't that much better, coming across as ruthless manipulative thugs who treat the Diamonds as expendable tools at best.

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