[1] Her novels and mysteries are set in England, France, and Wales, and are about English and Welsh royalty during the Middle Ages.

The Sunne in Splendour, her first book, is a stand-alone novel about King Richard III of England and the Wars of the Roses.

She had plenty of material to be written about the "rebellious sons and disgruntled brothers and conniving kings and willful queens" of the Plantagenets and hoped to write as many as a dozen books on the subject.

[6] After the publication of The Sunne in Splendour, Penman began work on the Welsh Trilogy, set primarily in Wales.

[6] The "Welsh Trilogy" was followed by the "Plantagenet series", which presents the events of the life of King Henry II and Eleanor of Aquitaine.

[15] The third novel in the series, The Dragon's Lair, is set during the same period, but Penman shifts the locale to northwest England and north Wales.

Falls the Shadow is a bridge novel as Penman uses the Simon de Montfort rebellion to lead her to the conclusion of the trilogy in The Reckoning.

[19] Penman's characterization of Simon de Montfort is that of a man increasingly disillusioned by his sovereign, who rebels in 1263, becomes regent to Henry III, and attempts to re-establish rights granted under the Magna Carta.

[20] In addition to the story of Simon de Montfort and his wife, Eleanor the Countess of Pembroke and sister to King Henry III, the novel presents characters such as the Welsh ruler Llywelyn Fawr and London's FitzThomas.

[19] The Reckoning (1991) chronicles the reign of England's King Henry III in Penman's final volume of the series that began with Here Be Dragons.

Additionally, Penman chronicles the life and character of Ellen, daughter of Simon de Montfort and niece to Henry III; her betrothal to Llewelyn (negotiated prior to de Montfort's death); and the conflict between Ellen and her cousin Edward, soon to become King Edward, who opposes the betrothal.

Their children were branded by contemporaries as "The Devil’s Brood," but they founded a dynasty that was to rule England for three hundred years.

[24]When Christ and His Saints Slept introduces the genesis of the Plantagenet dynasty as Empress Maude fights to secure her claim to the English throne.

[7] In the 15 years she spent writing three novels and four mysteries set during the period of Henry II and Eleanor of Aquitaine Penman claimed she found no villains.

[11] The Devil's Brood was supposed to be the final volume in Penman's Plantagenet series, but the "Angevins were not ready to go quietly into that good night.

The book focuses on Richard the Lionheart's Crusades in the Holy Land, and on what happened to Eleanor when she was finally released after spending sixteen years in a confinement that was ordered and enforced by her husband.

[11][23][24] A Library Journal review praises Penman's attention to detail in which she "combines an in-depth knowledge of medieval Europe with vivid storytelling, re-creating the complex events and emotional drama of the 12th – 15th centuries.