End of Book 7 summary: Callie Shaw has had it with the Hardys! Frank's girlfriend wants to know why she can't work with them. She's just as good an investigator as they are.
Storming home after an argument, she literally walks into an ambush—and a deadly test of her detective abilities. As more and more mysterious attacks are aimed at Callie, one thing becomes clear. This case had better be solved before she gets killed!
With the help of a beautiful young investigative reporter, the Hardys tackle one of the strangest cases of their career. Will they find the mysterious attacker? Can they save Callie? Or are they in too deep to save themselves?
Back cover summary: Frank Hardy's girlfriend, Callie Shaw, is determined to join him and Joe in solving crimes. So when she bumps into a mailman and mistakenly recovers a top-secret codebook, Callie thinks she's found the perfect case. She challenges the brother detectives to help her break the code. Trouble is, the real owner is deadly serious about getting it back.
Joe is knocked cold during a daring burglary, and when he comes to, the black book is missing. But not before Frank has uncovered a link to a secret network of fraud, corruption, and murder. It seems Callie has stumbled on to a major scandal—will Frank and Joe end up taking the fall?
Contains the following tropes:
- Actually Pretty Funny / Touché: Callie ribs Joe at the end by saying the main reason she knew "Lisa" had to be a phony was because of the way the latter kept shooting gaga-eyes at him. Joe protests for a second, but then joins Callie and Frank in laughing and admits she got him good.
- Assassins Are Always Betrayed: Inverted for fear of being played straight. Once Gina learns that her attempt to make Morrison's death look like a suicide didn't work and the coroners have ruled it a murder, she is determined to hunt down and kill the man who hired her for the hit job, certain that otherwise he'll quickly betray her to law enforcement if he gets caught. Saunders insists that he wouldn't do so, but she ultimately doesn't really care and decides to kill him anyway just to be safe.
- Big Damn Heroes: Callie gets to save the day at the end, having deduced that "Lisa" is the villain before the Hardys do, and shows up Just in Time to knock her out with a bat before she kills them.
- Character Focus: This is the first of quite a few books in the Casefiles to be heavily Callie-centric, such that she serves as the Deuteragonist to the boys' protagonists.
- Girl of the Week:
- Subverted in that the main girl of the book is Callie Shaw, Frank's girlfriend and a mainstay in the series, who plays almost as prominent a role as the boys themselves.
- Played straight, however, with Lisa Cantwell, Joe's love interest in this book who acts as the fourth member of the investigative team. Unfortunately for Joe, she turns out to be a Love-Interest Traitor.
- Humble Pie: Joe gets a taste of this throughout the book. After a long time of not taking Callie seriously as a detective mainly because she's a girl, and dismissing her desires to help him and Frank with their detective work, he meets and falls for a different girl, Lisa, with whom he greatly enjoys working as an investigative partner, while also having some tension with Frank about the latter's similar growing respect and admiration for Callie during the case. Then at the climax of the book, Lisa is revealed to actually be a ruthless contract killer named Gina who never cared for him, was using the boys all along, and almost murders them, only for them to be rescued by Callie, who figured out before they did that Lisa was the bad guy. To his credit, he does genuinely apologize and compliment her, and welcomes her to the team.
- I Ate WHAT?!: Frank, Joe, and Callie already hate the food that the school cafeteria has started serving this year after a new company got the contract. But they're completely disgusted to learn the full extent of why it's so bad: the "meat" dishes served at the school cafeteria (such as the hamburgers, meatloaf, and veal goulash) are actually made from horse meat, and other types of meat that are so disgusting that even dog food companies won't touch them. Similarly, the vegetables are literally rotten.
- I Have Many Names: "Lisa Cantwell" turns out to be an alias being used by a hitwoman, whose "professional" name is "Gina". Neither of these are her real name and we never actually learn what it is.
- Intrepid Reporter: Lisa is a skilled investigator just like the Hardys. Though this is subverted at the end, when she reveals that this was just her cover and she's really a hitwoman.
- Look Behind You: A variant when Frank pulls this on Gina at the end. There actually is someone behind her (Callie), but Frank is employing Reverse Psychology to make sure Callie doesn't get caught.
- Love-Interest Traitor: Lisa Cantwell, the investigative reporter whom Joe, Frank, and Callie befriend and who acts as a love interest for Joe, is revealed at the climax of the book to be a ruthless hitwoman known as "Gina", who was just using the Hardys. She's also more than a decade older than they are.
- Never Suicide: City manager Jack Morrison's death is initially ruled to be a suicide, but then the coroners discover evidence that he was murdered. The killer turns out to be Gina.
- Not an Act: Several times, Lisa puts on a very convincing "bad cop" routine to intimidate enemies, and justifies it to the others by saying she has to be a good actress for her investigative reporter work and is glad that she looks convincing enough. But at the end, once she's revealed to actually be a hitwoman and the true Big Bad, it's clear that these "tough gal" moments were some of the very few things about her that weren't an act.
- Older Than They Look: Gina takes heavy advantage of this. She's around 30 years old, maybe even older, but in her "Lisa" identity, appears to be in her early 20s, close enough to the Hardys in age to act as a love interest for Joe. And at one point as "Lisa", she wears a disguise that makes her look like she's around 17.
- Professional Killer: Lisa's/Gina's real profession. According to Saunders, she's a good one, too, enough so that her name is quite well-recognized within the industry.
- Reverse Psychology: When Gina has the Hardys cornered and is ready to kill them, they see Callie sneaking up behind her. Frank promptly pulls a Look Behind You, knowing fully well that Gina will think it's a pathetic bluff to try to distract her and make it a point to not turn around. This gives Callie enough time to knock her out.
- Speech Impediment: Elliot Saunders III, the Acme boss, has a major stutter. This allows Gina to recognize him as the man who hired her over the phone to kill Morrison.
- Stay in the Kitchen: Both of the Hardys, but especially Joe, have this attitude towards Callie in the beginning. Part of it is thanks to what happened to Iola at the beginning of the series and concern that she could be put in similar danger, but Callie still doesn't appreciate it and is determined to prove her worth as a detective in her own right. By the end, she does earn both boys' respect in her investigative skills, and while this trope does still remain in future books, it definitely becomes more downplayed, especially by Frank (as Frank and Callie do team up in investigations many more times in the future).
- Too Good to Be True: How Callie figures out that Lisa/Gina is the bad guy of the book, noting that too many of the things she's claimed feel a little too convenient and don't add up.
- Vitriolic Best Buds: Kicks off the very vitriolic relationship between Joe and Callie that appears throughout the series. At the very least, though, he does learn to respect her more after the events of this book.
