Elle Nicoll's "Playing with Mr. Grant" is a novel that intricately weaves themes of power, desire, and the dichotomy between personal and professional lives. The narrative embarks on a journey where boundaries are tested and the deepest facets of character are revealed. The novel's erotic tone is matched with a compelling psychological depth, making it a captivating read from cover to cover.

The story centers around Cassandra Clarke, a talented junior lawyer working at a prestigious London law firm. She is intelligent, ambitious, and quite adept at her job. However, despite her outward appearances, Cassandra harbors a complex inner turmoil rooted in her desires and her past. Her life takes an unexpected turn when she meets the enigmatic and highly influential partner, Mr. James Grant. Known for his strict professionalism and inscrutable persona, Mr. Grant is a protagonist that readers will find both intriguing and frustrating.

James Grant is not just a simple character, but a puzzle that Elle Nicoll masterfully constructs throughout the narrative. His interactions with Cassandra are laden with tension, not just of a sexual nature but also a clash of intellect and wills. Their relationship evolves through challenging cases, late-night meetings, and clandestine encounters that blur the lines between professional obligations and personal desire.

The author does a remarkable job in depicting a realistic and sometimes gritty representation of life in a high-powered law firm. The pressures, the politics, the necessity for an impenetrable facade are all portrayed with a vividness that enhances the dichotomies within the narrative. This setting acts as a crucible for Cassandra and James, pushing them to confront not just each other, but their own selves. It is a meticulous exploration of power dynamics and control, which often shifts hands, leading readers through an evocative roller-coaster of emotions.

Sexual tension is a driving force in "Playing with Mr. Grant," and Nicoll has approached it with a boldness that is both raw and elegant. The erotic scenes are tastefully written, intertwining seamlessly with the psychological and emotional currents flowing between Cassandra and James. These moments are not just about physical connection but are pivotal in peeling off the layers of the characters’ personalities and pasts.

The character development of Cassandra is particularly noteworthy. From a wide-eyed newcomer to a complex protagonist battling her inclinations and professional demeanor, her evolution is crafted with great care and introspection. Her character represents the modern woman — empowered yet vulnerable, tethered to the past yet striving towards the future. The narrative voice of Cassandra is powerful, her internal dialogues and the transformation of her viewpoints present a profound understanding of her struggle and growth.

Moreover, Elle Nicoll's prose is engaging and fluid, carrying the reader through the chapters with a rhythmic ease. The dialogues are sharp, often laden with undertones that reveal more than the characters are willing to outright say. Nicoll’s use of symbolism and imagery enhances the atmosphere, pulling the reader deeper into the settings and the states of mind of the characters.

However, while "Playing with Mr. Grant" thrives in character portrayal and erotic narrative, it sometimes wanders slightly too far into the personal dilemmas of Cassandra, which, while essential, occasionally slows down the plot. Some readers might find these introspective passages a bit prolonged, though they contribute substantially to the thematic depth of the novel.

In conclusion, "Playing with Mr. Grant" by Elle Nicoll is a provocative and intensely emotional novel that explores love, power, and identity in a modern world. Its strength lies in its complex characters and the explosive interplay between them. This book is a recommendable read for those who enjoy psychological depth blended seamlessly with eroticism, all set against a backdrop of a high-stakes corporate environment. As Cassandra and James navigate their dangerous game, we are reminded of the fine line between control and surrender, making this novel not just a story but an experience of confronting one's own boundaries and desires.