It focuses on an eleven-year-old boy named Ben, who likes history and wants to be a plumber but cannot dance, staying with his granny while his parents (who love ballroom dancing) go to a concert.
The granny likes crime novels, which Ben is interested in, but Granny's other interests (feeding ducks, Scrabble, etc) he finds boring and he dislikes her cabbage-based recipes.
When he finds what appear to be jewels in her cookie box, she tells him about how she used to be an international jewel thief, which makes Ben make a huge plan to steal the Crown Jewels.
It is mostly a humour book but there are some serious moments and a sort of moral about how elderly people aren't boring.
Gangsta Granny provides examples of
- Action Girl: Despite being elderly, Granny is very fit and even climbs down a skyscraper at one point.
- An Aesop: "Elderly people aren't boring".
- Also "Appreciate your family while you can."
- Alliterative Title: Gangsta Granny.
- Amazingly Embarrassing Parents: Ben finds his parents embarrassing because they get him to dance even though he can't and make him wear crazy outfits.
- Ass Shove: Ben talks about how people used to get penalized with a "red hot poker up the bum" way back when.
- Baby Talk: One of Granny's annoying habits is using baby talk with Ben even though he's eleven (she uses the word "beddybyes" for instance).
- Character Death: At the end, Granny dies of cancer.
- Character Title: Granny is mentioned in the title.
- Comedic Underwear Exposure:
- At the end of the book, the queen flashes her underwear.
- Earlier on, Granny does her so-called "naked yoga" in her underwear.
- Cool Old Lady: Zigzagged. At first, Ben finds the granny boring. Then, he finds her cool with her past as a jewel thief. This turns out to be a lie, but it turns out she's pretty darn cool anyway.
- Cordon Bleugh Chef: Granny is a competent chef, but tries to put cabbage into everything, even desserts.
- Does Not Like Spam: Ben doesn't seem to like cabbage.
- Embarrassing Nickname: Ben thinks Granny's nickname for him (Benny) is too babyish.
- Extreme Omnivore: Downplayed for Granny, who doesn't mind eating spoiled cabbage.
- Feeling Their Age: Subverted. Granny thinks she's too old to swim up a sewer pipe but she's not.
- Gasshole: One thing that Ben doesn't like about Granny is how she farts an awful lot and said farts smell of rotten cabbage.
- Tear Jerker: Granny telling ben that she has cancer.
- Getting Crap Past the Radar: One joke is about Ben's mum thinking he's hiding a "naughty magazine" under his bed.
- Girls Have Cooties: When Ben's mother thinks he's "expressing an interest in girls", he calls girls gross.
- Gosh Dang It to Heck!: "Bums" is treated as a swear word.
- Granny Classic: Zigzagged for Ben's granny. At first she's just a stereotypical granny who has false teeth, knits sweaters her grandson doesn't like, etc, but then she talks about being an international jewel thief. This turns out to be a lie, but she does turn out to be more active and crafty than a stereotypical old lady.
- I Lied: When confronted by the Queen, Granny admits to having lied about being a jewel thief.
- In-Series Nickname: Granny calls Ben "Benny".
- Mistaken for Thief: Invoked for Granny, who lies that she's a jewel thief.
- Needlework Is for Old People: One of Granny's habits Ben doesn't like is knitting him sweaters with puppies and kittens on.
- Nightmare Fetishist: Ben really likes the gory parts of history (he mentions being hanged, drawn and quartered several times).
- No Name Given: We're not introduced to Ben's parents or his grandfather.
- Nosy Neighbor: Granny has a neighbor who likes to look through her window.
- Old Master: The granny is able to do many action things, including abseiling down the side of the hospital building with bed sheets.
- Plot Allergy: Nobody is actually allergic to anything, but the narrator says that if anyone was allergic to cabbages, they wouldn't be able to be near Granny because she always has cabbage smell on her breath.
- Sick Episode: It turns out that the granny has cancer.
- Technologically Blind Elders: Neither Granny nor the Queen know what "Googling" is.
- Toilet Humour:
- One of the details of history Ben likes is people getting red-hot pokers up their butts.
- Granny farting is a running joke.
- Granny uses "Big hairy bums!" as an exclamation.
- Ben and Granny swim up a sewer pipe and end up "smelling of poo-poo".
- There is one joke about a lord burping.
- Granny claims that she once stole a diamond ring, swallowed it, and pooped it out.
- The Topic of Cancer: When Granny reveals she has cancer, Ben is instantly afraid for her life and eventually, she does die.
- Unnamed Parent: We never find out the names of Ben's parents or Granny.