At the heart of Susie Dent's contemporary mystery masterpiece, Guilty by Definition, lies the unfinished story of the Thornhill sisters, two academically gifted women with opposing temperaments and a shared passion for the written word. The eldest, Charlotte, went missing more than a decade ago from her family home in Oxford, England, while working on her PhD. Her case remains unsolved. Charlie, as she was known, was gorgeous and charismatic in an intimidating, sometimes cruel way; her shy younger sibling, Martha, languished in the shadow of her sister's brilliance. The radiating energy of Charlie's "living absence" haunts the pages of Dent's marvelous novel as her fate comes clearly into focus.

The story opens one spring with Martha, now in her mid-30s, returning to Oxford after a decade abroad in Berlin. She fled her hometown after Charlie disappeared--it was too painful to remain--but now she is back as the newly appointed senior editor of the Clarendon English Dictionary, with a talented team of lexicographers under her supervision. Soon after she joins the CED, anonymous letters containing perplexing riddles and Shakespearean clues begin arriving at the dictionary office. While the missing Charlie is the apparent focus of the letters, they also allude to an ancient manuscript that, if it exists, will spark a global literary sensation. It's an intriguing and irresistible premise set against the enchanting backdrop of Oxford's "obligingly dreamy" architecture.

Dent (Word Perfect; Dent's Modern Tribes), a renowned English lexicographer and etymologist, is the popular, longstanding resident word expert on the British television show Countdown and has authored a number of books on the English language. Her first novel captures the seductive power of the written word, bound up as it is with history, cultural meaning and literary references, its ability to encapsulate a time and place long gone. Intimately familiar with Oxford, she is a guide through its "twisting cobbled alleyways" and the fascinating inner workings of the CED, modeled on Dent's prior employer the Oxford University Press. This is where Martha and her team record new words that come into existence and document the evolution of existing words.

Readers with a fondness for word games will have a splendid time trying to decipher the cleverly confounding clues and the letter writer's identity in the excellent company of Martha and her three colleagues, who share a passion for etymological challenges and obscure literary references. There's Simon, senior to Martha in tenure, who was passed over for the senior editor position and wears bright patterned shirts to the office. Alex is a brilliant woman, older than Martha, with an exquisite sense of style and a secretive life outside the office. The youngest lexicographer is the quick-witted Safi, known for her bright outfits, her fierce intellect, and her impressive mastery of the finicky printer. All are pulled together by Martha, whose gentle pre-Raphaelite beauty contrasts with her absent-minded fashion sense and the Doc Martens she pairs with her dresses. Her team is accustomed to receiving the odd "Shakespearean crank letter" now and again, but the new anonymous correspondence portends something more serious and casts an unsettling pall over the office, especially when the lexicographers start receiving cryptic postcards at their home addresses.

As Martha reacquaints herself with favorite Oxford haunts, she must also confront relationships that she has neglected, especially with her widower father, who resents Martha as though she is to blame for Charlie's disappearance. Echoes from the past are everywhere, urging her to find Charlie or discover her fate, reminding Martha of the role she fears she played in her sister's disappearance.

Fueled by Safi's crackling enthusiasm, Martha and her colleagues begin in earnest to decipher the anonymous letters as they gather in the office and in a 14th-century pub tucked into an ancient courtyard. Their investigation takes them to the Cheshire Cat Antiquarian Bookshop in the Cotswolds and a manor house in Oxfordshire Charlie had visited. Martha enlists the help of Detective Oliver Caldwell, convincing him to reopen Charlie's case, and she asks the pompous Shakespearean scholar Jonathan Overton--handsome, beautifully dressed, and disagreeable--for help deciphering the letters' mind-boggling clues. Dent's skillfully executed plot holds multiple layers of tension, including the relationship dynamics of a tight-knit yet secretive literary community. Not everyone is thrilled that the case is reopened, and it soon becomes frighteningly clear why.

Part of Guilty by Definition's charm lies in discovering, alongside Martha, Simon, Alex, and Safi, intriguing lost words. Each chapter is headed by a forgotten word from past centuries: the noun "velleity," for example, from the 17th century, means "the act of wishing or desiring without any accompanying effort"; the marvelous 16th-century word "addubitation" means "a suggestion of doubt."

Swirling with themes of sibling rivalry, greed and ambition, the novel's action accelerates as clues contained in the letters give way to newly uncovered truths and lead to a heart-pounding, spectacular finale. The mysteries at the center of the drama--Charlie's whereabouts and what she was hiding, Martha's guilt, the identity of the letter writer--find resolution in a series of unexpected yet ingenious plot twists that will take readers utterly by surprise. --Shahina Piyarali

Susie Dent (photo: Michael Leckie)

Susie Dent, lexicographer and etymologist extraordinaire, lives in Oxford, England, where her first novel, Guilty by Definition (Sourcebooks Landmark, September 30, 2025), is set. She is a beloved English television personality who has appeared on the British game show Countdown since 1992. The author of several nonfiction titles, including Word Perfect, How to Talk Like a Local, and What Made the Crocodile Cry: 101 Questions About the English Language, Dent was appointed a Member of the Order of the British Empire (MBE) in 2024 for her contributions to language and literature. Guilty by Definition is set in a tight-knit literary community still haunted by the disappearance of a brilliant PhD student a decade earlier. The unraveling of that mystery is coupled with the search for a lost treasure trove of writing that, if it exists, will transform the literary landscape.

What are some of your earliest memories of interacting with words?

I have been intrigued by words for as long as I can remember. As I child, even before I was able to read, I was fascinated by the letters on signposts and shampoo bottles--by their shape and promise. In a way, it's always felt as though words found me rather than the other way round.

Are there aspects of yourself in Martha, and are there parallels between her life and yours?

Martha is very similar to me in lots of ways. She is a daydreamer and lives in her head; she marvels at the secret lives of words, and sees the beauty of German, having lived in Berlin for a while, as I did. But I did also try to draw some distinctions between her character and mine. She is not a worrier, as I am, and she can be unintentionally blunt, whereas I tend to apologize too much! I do tend to think of her as a soulmate, however, and often find myself wondering what she might make of conversations or encounters that I experience.

In our age of digital storage, there's something solid and reassuring about the slips of paper bundled with string at the dictionary office. Are slips still used to record the biography of words?

The "slips" room at Oxford University Press, home of the Oxford English Dictionary and the inspiration for the dictionary in my novel, is a place of wonder. As a room, it's pretty ordinary, but the magic begins when you take down a stack of slips--6×4 pieces of paper stored in weathered oak cases--and begin to read the jottings of lexicographers of the past and the evidence they collected for how words are used. The first editor of the OED, James Murray, built a shed in his garden in Oxford to house the thousands of slips from his team of editors and readers, which he called his Scriptorium. Today's lexicographers still consult the evidence of language usage from previous editors when revising existing entries, although much of today's dictionary-writing is, of course, fully digitized. We are able to consult vast databases containing billions of words of current language, allowing us to document change in real time.

Safi, with her youthful energy, is the youngest of the lexicographers we meet at the Clarendon English Dictionary. Are millennials and Gen Z entering the profession?

Very much so. The passion for documenting language that I wanted to illustrate through Safi is as strong as ever, and lexicography continues to be a hugely exciting profession. It is vital that it attracts younger generations who are not only immersed in current language evolution but who are also best placed to monitor words that are bubbling under--for example from current slang--and which might burst through the surface at any moment.

Do you still encounter unfamiliar words after all this time immersed in the English language and its history?

I learn something new every day! I can't imagine I will ever tire of reading the dictionary and delighting in the history of even the most everyday words. Today I've been looking at "kennings," word couplings that date back centuries and that describe everyday things. A ship, for example, was once described as a "wave-horse," the mind was a "thought-chamber," and a "sea-candle" was the sun as it dips below the horizon over the sea. They're so beautiful.

With Guilty by Definition poised for an outstanding reception, will you continue writing fiction?

This was such an exciting new direction for me after many years of writing nonfiction, but it was also a scary one. The prospect of creating a fictional world populated by complex characters was quite intimidating, quite apart from the plotting!--but I am so glad I took the plunge. I am learning all the time in this new medium, and very much want to discover where Martha and her team will go next. There will be a second novel next year and, if readers enjoy it as I hope, more after that.

Can you share any advice or organizational tips for fledging fiction authors?

Two pieces of advice from writer friends turned out to be really valuable. The first was to write about what you know, which certainly made things less daunting. There is a lot of linguistic exploration in Guilty by Definition, and its story also gave me a chance to share some forgotten words from the past that I adore. The second was to write the first draft with as much spontaneity and unselfconsciousness as possible, as so much of the work is in the edit. The plot, characters, and prose can all be remoulded later on. That made the initial blank piece of paper far less terrifying.

What is your version of an ideal day?

No alarm clock, excellent coffee, a cold sunny morning (so that I can use my favourite word, "apricity," which in the 17th century meant the warmth of the sun on a chilly day), then a few hours of reading followed by a long walk in the Cotswolds. The day would be topped off with a delicious supper with family and friends, chatting into the night long after the eating is done--what the Spanish know as sobremesa: relaxing at the table after a meal. That would be my perfect day! --Shahina Piyarali