Is Alistair Oh an old man who genuinely cares for Amy and Dan and feels regret for leaving them for dead time and time again and being there when Isabel set the fire that killed their parents, or a backstabbing enemy who feels no remorse for his betrayals?
Ian Kabra tends to be subject to this for several reasons, but since his going rogue in The Dead of Night, the question of his true nature is definitely up for debate. However, it turns out that his departure had nothing to do with any form of betrayal (except his mother's) and that The Mole was actually Sinead Starling.
Angel/Devil Shipping: The very popular Amy/Ian pairing. Amy is one of the most moral cluehunters, while Ian is one of the most ruthless ones.
Archive Panic: With 26 books from the main series, 5 stories from the Cahill Files, the 7 part Rapid Fire ebooks, 2 handbooks, a prequel to the entire series, and a crossover, while they’re all fairly small books, the quantity really adds up.
The trading cards and website, especially the cards. Why? In the opinion of many fans, the pictures of the characters on the trading cards do not live up to the characters' descriptions in the books or the way that readers imagined the characters to look like, or else simply do not look appealing (a common complaint is that Ian and Evan look too much like Justin Bieber). The rest of the fans either like the pictures on the trading cards, or just like the trading cards and couldn't care less about what the pictures look like.
When the official message boards were made canon in The Dead of Night, some fans blew a gasket. Others eagerly played along with Evan's posts on the message boards. It's hard to find someone without a clearly defined opinion on this development...
The exclusion of the Rosenblossom brothers in the fourth series, Doublecross. Was it beneficial, as they were scrappies that kept badgering the plot, or a terrible idea, as they brought levity to the story?
Fans of Amy/Ian have been known to behave extremely aggressively towards any and all opposing pairings, bashing Hamilton, Kurt, and Evan, complete with a plethora of Revenge Fic for the latter two.
It is difficult to find a fan who does not believe that the infamousKurt, who briefly appeared in one book and was never seen again, was an undercover Vesper.
A friend of Amy and Dan's Uncle Shep was mentioned once in the first series. But due to his name (Gregory Tolliver) and the revelation that Arthur Trent, Amy and Dan's father and Shep's cousin, was a Vesper, people not only believe that this friend is probably a Vesper, but that Evan Tolliver is related to Vespers as well (if not a full-blown undercover agent). This fandom sure does love its Epileptic Trees...
Since the revelation of Isabel Kabra's maiden name (Vesper-Hollingsworth) and of the fact that Arthur Trent is a Vesper, a great deal of fanon involving them has sprung up. It's taken for granted that they interacted with each other when younger, and many fans believe that they were romantically involved, though there is no canon basis for this. (Although the fact that Isabel knew about the "moon face" thing that Arthur and Dan used to do, enough to use it to manipulate Dan with the "AJT" texts, may imply that they were close.)
The idea that Vikram and Hope were once an item has also gained some acceptance among the fandom.
Quite a few fans are absolutely convinced that Amy's full name is Amy Hope Cahill, seeing as her brother's full name is Daniel Arthur Cahill.
It's also popular to think that "Amy" is a nickname for "Amelia." While the former can be a shortened form of the longer name, it can also stand on its own.
It's generally accepted that Amy and Dan got their green eyes from their mother, and although Canon gives no evidence supporting this theory.
In the first series, Amy and Dan were often shown to have sibling telepathy, but that has all but disappeared in the Sequel Series. It is because, as Dan grows darker and more emotionally distant from his sister, he and Amy can't understand each other as well as they used to.
The Black Book of Buried Secrets has sections listing the skills and tricks used by each branch—except the Madrigals. Because the Madrigals presumably use all of them!
Ian's famous "Shoot to kill?" line in The Medusa Plot is suddenly not so funny anymore after Evan is actually shot and killed at the end of the Sequel Series. After he and Ian seemed to have been starting to develop a friendship, no less.
The ending of The Sword Thief, where Alistair fakes his death to escape and later in the first series, when he pretends to die of heart failure to trick his Evil Uncle, are not nearly as amusing after reading Trust No One, where he dies as a result of a seizure.
Ian's thoughts when his sister is kidnapped aren't exactly uplifting to begin with, but they become even more painful after she dies, along with their estranged mother.
It was funny... [Ian] didn't even like Natalie. But now that Mum had disowned them and Father was out of the picture, Natalie was his whole family.
Ian and Natalie become this after they undergo a lot of Character Development. And their scary mother shows up... and eventually tries to kill them, along with the other Cahills.
Ian specifically has it worse by the end of the Cahills vs. Vespers series. His sister, the only person he really had left, is killed in Day of Doom. Their mother, Isabel, finally shows a shred of humanity upon learning of Natalie's death—but in her rage, she drinks the master serum and ends up dead, as well (though not without a glorious Dying Moment of Awesome). His father is still in hiding and seems to want nothing to do with him. And that's probably just the tip of the iceberg, considering all the issues that being raised by Isabel left him with, as well as the fact that not everyone in the Cahill family completely trusts him yet.
Then, in fanon, we have Sinead Starling. The most popular Sinead ships are Sinead/Hamilton and Sinead/Jonah, but she has also been shipped with Casper Wyoming and occasionally Ian, and even fanfiction shipping her with Dan Cahill, Ned, or Amy have made appearances.
The Vespers crossed it at the start of their story arc by kidnapping the Cahills' loved ones (including both of Amy and Dan's legal guardians) to Blackmail them into committing a series of heists across the globe.
J. Rutherford Pierce crossed it with his Evil Plan to detonate a series of hidden nuclear bombs across the planet, kickstarting World War 3 and killing countless innocents. With the world in chaos, Pierce would dominate the globe with his army of serum-addled Super Soldiers, all while painting himself as a savior. Even after his bid for presidency is ruined, Pierce refused to disable the nukes, instead opting to let them detonate out of spite.
The Outcast not only attempted to recreate four of history's worst disasters whilst challenging the Cahills to stop him; he deliberately caused the originalChernobyl disaster to cover up his own illegal activities, and was more than willing to do it again on an even larger scale.
Mr. Burnam; the Outcast's incompetent butler, crossed it when he dropped Saladin off at a pet shelter to be euthanized, then sadistically gloated about it to Amy.
Romantic Plot Tumor: In Day of Doom, especially with the by now infamous Amy and Jake Love Confession in the closet scene. Even many of the pairings' supporters found its portrayal in that book to be cheesy, OOC, and ill-timed.
Quite frequently for Evan Tolliver and Kurt. The most commonly found demonization is making them turn out to be undercover Vespers, but fanfiction involving Evan suddenly dumping Amy is also becoming common.
Luke Cahill is sometimes treated this way, for no apparent reason other than he liked to sneak around more than his siblings. He did also become somewhat of a Jerkass in his later years, but he was never evil.
When Dan failed to drink the master serum because of Amy and Isabel preventing him, it was deemed a wasted opportunity to explore themes of absolute power's corruption and morality. This plot line returns with a vengeance, with Amy drinking the serum in "Countdown". As a result, her story onwards from that point was loved by fans, who thought her struggles with the physical and psychological effects of the master serum were compelling to read about.
The surprisinglyhappy ending, with the world saved, and Amy and Dan happily heading off to resume their lives, was mocked due to its ignorance of all the heavy emotional scarring that the Vespers' presence would bring. The first book of this series, "Nowhere to Run", showed, right off the bat, that Dan and Amy are not okay with how the Vespers manipulated them, as they harbor PTSD over this. Not only that, they have been having tutors instead of school, just so they can feel safe.
The Romantic Plot Tumor of Amy and Jake getting together was savaged for the OOC moments that it created for Amy, the Love Confession being written cheesily, and the mere notion that by "Day of Doom", Amy still wanted to continue her newly-budded relationship with Jake, despite her former boyfriend Evan dying just days ago. A subplot was created for this series, with Amy repeatedly trying to force Jake away to keep him safe, and remain Just Friends, as she clearly still grieves for Evan. Whether this worked is up for debate.
Shocking Moments: The Reveal of Cara Pierce actually being April May. Absolutely no one predicted this, always assuming that they were two separate people.
Surprisingly Improved Sequel: The third series, Unstoppable, set to right a few wrongs from the second series, "Day of Doom":
The Evil Plan of the Vespers (Using a Doomsday Device to destroy the world) was deemed too cliché. This time, the main villain's plan is to mass-reproduce the master serum for him and his closest allies, then become the United States President and start a new World War to garner support for him. This was seen as superior.
The killing of minor and major characters (William McIntyre, Erasmus, Luna Amato, Alistair Oh, Natalie Kabra, Evan Tolliver, Isabel Kabra and Damien Vesper III) was criticized for being too dark, cheap ways to raise the stakes and complete wastes of interesting characters. In this series, while there is only one minor character who dies (Pony), no other significant characters bite the bullet by the end, which was praised, because the stakes were still high without needing to resort to pointless deaths.
The Man in Black/Fiske Cahill. After his reveal in Storm Warning, namely being Amy and Dan's long-lost grand-uncle, the only time he gets to show off his Cahill skills was in Vespers Rising. Despite this, for the rest of the series, he ends up being kidnapped by Isabel Kabra, the Vespers and J. Rutherford Pierce, and has an unnamed sickness for the fourth series, putting him out of commission. His past was only dictated in one short story (The Submarine Job) and a tie-in book, and nothing more.
Broderick Wizard. Trading cards and supplementary material implied that he was actually a Vesper. This idea could have been further explored instead of being abandoned, since he always loves Jonah when his wife was more strict, and this Vesper plotline could have thrown a wrench in this relationship.
Natalie Kabra. The first series had intriguing ideas for her: being someone who learnt to trust her older brother and realising that her branch, mother and father were not as kind or well-intentioned as they were. The second series ends up making her nothing more than a hostage for the Vespers, and only uses her for comedic purposes, such as her horrified reactions when she had to remove a bullet from Nellie. Even worse, her death at the end of that series is undignified; grabbing the Idiot Ball by whacking the activated Machina Fini Mundi machine with a pipe, causing her to be electrocuted.
Dan and Amy have a lot of Heartwarming Orphan angst, especially given the trauma they go through during the cluehunt, and in the wake of the death of their last loving relative, too.
At least towards the end of the series, Ian and Natalie. In the beginning, they were quite cruel. But after we meet their mother..., their Freudian Excuse invites readers' sympathy.
