Elizabeth I has bewitched and eluded biographers in equal measure. The daughter of Henry VIII’s second wife, Anne Boleyn, her birth in 1533 is inextricably linked with one of the most momentous constitutional changes England witnessed between the Norman conquest and the Brexit vote. She was, as Helen Castor writes in this crisp contribution to Penguin’s miniature Monarchs series, the “living embodiment” of the religious revolution that brought about the break with Rome and made her father head of the Church of England. Both the young princess and the fitful and idiosyncratic process we call the English Reformation were byproducts of Henry’s sexual whims and desperate desire for a male heir. Elizabeth’s childhood, adolescence and early adulthood were lived in the shadow of the recrimination and violence these events unleashed.

Taking on Elizabeth is no easy task. This is not merely because she has been the subject of so many books and featured in so many films. Her capacity to be endlessly reinvented is a function of her enigmatic character. Her recorded words and actions are ambiguous. Wisely, Castor does not sidestep this intrinsic difficulty. She acknowledges Elizabeth’s emotional opacity and makes this integral to her analysis. As she remarks, the inscrutability of the queen is compelling evidence itself.

Elizabeth's ​frustration is nicely encapsulated in the image of her randomly stabbing ​​tapestries with her sword

Elizabeth mastered the art of hiding in plain sight and elevated dissimulation and delay into statecraft. Behind “the carapace of a carefully constructed public self” was a psyche that Castor suggests was deeply scarred by the traumatic fact that her mother had been killed on the orders of her own capricious father. This is largely an argument from silence, but one precious and poignant object (reproduced as one of eight coloured plates) gives it weight: an exquisite mother-of-pearl locket ring dating from c1575, which opens to reveal Elizabeth’s own portrait paired with Boleyn’s.

Castor’s subtitle is “A Study in Insecurity”, and central to her account is an emphasis on the profound precariousness of Elizabeth’s experience at both personal and political levels: from the dysfunctional stepfamily in which she spent her early years to the fraught world of domestic conspiracy and international intrigue that formed the backdrop to her 45-year reign. Out of this came a resolve and self-control that disguised her vulnerable humanity. This enabled her to resist the pressure to marry and solve the succession problem, and to sit out crises through a canny strategy of “watchful inaction”.

Elizabeth’s youthful flirtation with Thomas Seymour and her relationship with Robert Dudley, Earl of Leicester, receive due attention, as does the chess game of court politics she conducted with her privy councillors, repeatedly finding space for her own priorities by refusing to move. The anger and anguish she experienced after being manoeuvred into signing the death warrant of her Catholic cousin Mary Queen of Scots in 1587 is brought out particularly well. Weeping, raging and refusing to eat or sleep, she banished William Cecil, Lord Burghley, from her presence for months in a fit of pique. Other familiar episodes also find a place in this abbreviated account, including Elizabeth’s tribulations in the reign of Mary I and her famous speech at Tilbury camp on the eve of the attempted invasion by the Spanish Armada in 1588. In stressing the “impressive sang-froid” and poise with which she navigated these challenges, Castor is not immune to the overestimation of her subject that is the occupational hazard of biographers. She captures something of the shifting dynamics of the 1590s, a decade marked by the death of the queen’s most trusted advisers and fractious parliaments that left her increasingly isolated. Her frustration is encapsulated in the image of her randomly stabbing tapestries with the sword she kept close to hand. Yet more might have been said about the growing mood of resentment and disillusionment that set in with the rule of a grumpy old woman.

A more significant lacuna in this account relates to Elizabeth’s religious outlook. Castor evades the knotty question of what kind of Protestant she was, and in presenting the ecclesiastical settlement of 1559 as an attempt to pursue a “middle path” she accords an agency to the queen that may overlook the role of the pressure groups by which she was surrounded and on which the reversal of Mary’s Counter-Reformation relied. Castor alludes to Elizabeth’s famous refusal to make windows in the souls of her Catholic subjects by requiring only outward conformity to Protestantism, but her struggles with zealous Protestants determined to purge the English church of the remaining vestiges of popery are almost completely occluded.

Perturbed by the queen’s lukewarm commitment to the God-given task of further reform, puritans offered a robust critique of the religious proclivities of the regime. A bite-sized biography such as this must be selective, but Elizabeth’s distaste for clerical marriage, old-fashioned liturgical preferences, and stubborn refusal to countenance attempts to reconstruct English Protestantism in the image of Calvin’s Geneva are curious omissions. Closer attention to them might have reinforced and refined the picture of studied procrastination in the face of instability that Castor paints.

Engaging and well-written, this little book is, however, a neat synthesis of scholarship on Elizabeth’s life with an interesting angle. Its chief merit is to approach her unreadability less as an obstacle than as an opportunity.

• Alexandra Walsham’s Catholic Reformation in Protestant Britain is published by Ashgate. Elizabeth I: A Study in Insecurity is published by Allen Lane. To order a copy for £11.04 (RRP £12.99) go to guardianbookshop.com or call 0330 333 6846. Free UK p&p over £10, online orders only. Phone orders min p&p of £1.99.