In the twilight years of her reign, Elizabeth I was not allowed to appear as an old woman: she had to remain Gloriana, reliant on wigs and paint and costumes to sustain the illusion. Equally, Jeanne de Musset, the titular heroine of Sarah Gristwood’s The Girl in the Mirror, is unable to appear as a young woman. A child refugee from massacres in the Low Countries, she is reared as a boy and develops a passion for plants and gardens. She finds employment in the house of Robert Cecil, Elizabeth I’s trusted adviser, where, as she soon discovers, ‘reflection and illusion’ are paramount. Loyal to Cecil, she is nevertheless as susceptible as the old queen herself to the charm and brilliance of the young Lord Essex, and Jeanne/Jan is caught up in the unfolding tragedy of his final months. Gristwood, previously a biographer, knows the Elizabethan world intimately; she has made use of a legend that grew up around Essex’s last desperate attempt to evade execution and which provides the climax to this absorbing tale – though occasionally she seems to find it hard to resist the historian’s love of analysis and allow the story itself to unfold.

Why do biographers turn to fiction? Is it because they are frustrated by the inevitable gaps and guesswork, and long to enter their protagonists’ minds? Stella Tillyard, who has been hugely successful with non-fiction