That Last Secret by Jenn McMahon is a thriller that expertly navigates the treacherous waters of deception, suspense, and the deep, often dangerous currents of family secrets. McMahon, known for her compelling storytelling and ability to draw readers into her meticulously crafted worlds, delivers yet another page-turner that's both enthralling and hauntingly resonant.

The novel is set in a small, seemingly idyllic town that holds darkness just beneath its surface. At the heart of this darkness is the story of Beth Lowell, a woman who has spent her life trying to outrun her past, only to find that her carefully constructed world begins to unravel when a mysterious letter arrives. The letter, containing just five ominous words, "I know what you did," sets off a chain of events that pulls Beth back into a past she has fought desperately to forget.

McMahon's narrative structure is intricate, weaving between past and present to tell the stories of multiple characters connected by a sinuous thread of small decisions that lead to monumental consequences. This layering of timelines is handled with finesse, maintaining clarity and tension throughout, and enriching the reader's understanding of both character and plot as the story progresses.

One of McMahon’s great strengths is her character development. Beth, as the central figure, is crafted with depth and complexity. She is flawed, relatable, and ultimately sympathetic, which makes her journey compelling. The secondary characters are equally well-drawn, with distinct voices and believable motivations that weave neatly into the larger storyline. As secrets begin to surface, the interactions between characters tighten, creating a palpable tension that drives the narrative forward.

The themes of That Last Secret are dark and often troubling, dealing with issues such as betrayal, guilt, and the lifelong impact of trauma. McMahon handles these difficult subjects with sensitivity and a keen insight into human psychology, ensuring that the story resonates with emotional truth. The suspense is built not just around the actions that the characters take but also around the internal moral reconciliations they must make. McMahon challenges her readers to consider not only what they would do in a similar situation but also the ethical dimensions of their choices.

The plot of That Last Secret twists and turns with expertly timed reveals and shocking discoveries. Just as the reader thinks they have grasped the nature of the secret at the heart of the story, McMahon introduces another layer that deepens the mystery and keeps the pages turning. The pacing is relentless, propelling the story forward with a sense of urgency that makes it hard to put down the book.

The settings in the novel—both the small town and the varied individual locales such as Beth's home, a rundown bar, and a secluded beach—contribute effectively to the atmosphere. McMahon employs descriptions that are rich in sensory details, which enrich the mood without overwhelming the reader or detracting from the action. The locale becomes a mirror for the characters’ lives, reflecting both the calm surface and the turmoil that lies beneath.

Moreover, McMahon's prose is sharp and evocative. She has a knack for choosing just the right word or phrase to convey an entire spectrum of emotion or to paint a vivid picture. Her dialogue is crisp and natural, providing clear voices for each character and enhancing the realism of her narrative. This careful attention to language not only enriches the reader's experience but also elevates the overall tone of the book.

In conclusion, That Last Secret by Jenn McMahon is a masterful blend of suspense, psychology, and human drama. It delivers both as a thriller and a probing character study, making it a compelling read for anyone who appreciates deeper, more introspective narratives alongside their suspense. This novel is a testament to McMahon's prowess as a storyteller capable of crafting worlds that are as deeply disturbing as they are impossible to put down. Whether you are a longtime fan of thrillers or a newcomer to the genre, this book promises not only to entertain but also to linger in the mind long after the last page is turned.