Brother Cadfael is pleased to join his young friend Mark, now a deacon, on a mission of church diplomacy in Wales.

Travelling in the safety of the Prince of Gwynedd's train, they are brought to unexpected dangers, as they seek to keep a young Welsh woman free from harm.

Second is the young woman Heledd rejected by her canon father in reaction to imposition of the Roman rite, sending her to find love among historic Welsh enemies.

From Llanelwy to Bangor, they travel in the train of Owain Gwynedd, stopping at his royal seat at Aber overnight, where Cadfael finds a murdered man.

In a scheme to regain his lands and his good standing with his brother, Cadwaladr makes a deal with the Danes in Dublin to threaten Gwynedd.

Owain rejects it outright, telling his brother he must make good his debt to the Danes and keep the three captives safe.

Gwion, returned on his own with supporters of Cadwaladr, does not succeed in freeing him, but sparks a battle, which kills three of the Danes, and some of his own men.

Owain arrives after dawn, with the drove of cattle finishing Cadwaladr's debt, seeing the Danes in full battle array.

They stay at Hugh's manor in Maesbury overnight for a pleasant family visit, with Aline and young Giles to cheer them.

Unlike most of the Brother Cadfael chronicles, the Summer of the Danes is set in north Wales, specifically Gwynedd.

Their encounter was at Abermenai Point, opposite the southwest corner of the Isle of Anglesey; Cadwaladr came with a group of Danes from Dublin[5][6] in his hope of again being in his brother's good graces and perhaps regaining his lost lands in the north of Ceredigion just south of the border with Gwynedd.

After the instance in this novel, Danes from Dublin acted in Welsh affairs, specifically after Owain's death in 1170, on behalf of his dispossessed son Hywel.

Prior to that, in the Great Revolt of 1166, Danes from Dublin were hired by Henry II of England to harass the coast while his armies fought the Welsh on land.

Another driving force of the story is the tension within the Church, represented at the time by Theobald, the Archbishop of Canterbury, and churchmen in Wales who wished to preserve independent Celtic organisation and forms of their Christian religion.

The See of St Asaph was reestablished the year before the story; Theobald appointed a Norman to impose the doctrines of Rome.

Deacon Mark alludes to the Claim of Metropolitan Status of the See of St Davids,[7] which would make it equal to Canterbury.

Mark and Cadfael walk west along it in search of Heledd; Turcaill brings his boat down it seeking food for the men; and Owain brings his troops so quickly overnight from Carnarvon to the west end of the Menai Strait where the confrontation with his brother and the Danes from Dublin occurs, at Abermenai.

A quick review of sounds with audio samples gives clear examples, including some of the names used in this book.

[12][13] One feature of this novel is the supper feast at Aber hosted by Owain Gwynedd, explicating the customs there by courses, by conversations and by placement at table.

[14][15] The courtesy due a guest in his house guided some of Owain's rapid decisions when the murdered man is found after the feast.

Kirkus Reviews finds this story heavy going, in contrast to earlier stories in the Cadfael series: It's the summer of 1144, and Brother Cadfael, herbalist-sleuth of Shrewsbury's Benedictine Abbey, has joined wise young Brother Mark on a diplomatic mission to newly installed Bishop Gilbert of St. Aspath's Church in Wales.

Cadfael, Mark, and another traveler—rebellious Heledd, daughter of Canon Meirion, on her way to an arranged marriage—are captured by the Danes and held hostage.

Densely packed with Welsh names and stately conversations, this isn't one of Peters's more vivacious efforts (Flight of a Witch, p. 441, etc.).

Kirkus Reviews Issue: June 1st, 1991[16]Library Journal reviewing an audio version finds Cadfael's role in this story different from prior novels in the series: When Brother Cadfael is excused from his duties at Shrewsbury Abbey to accompany Brother Mark on a mission of church diplomacy, he considers it a wonderful stroke of good luck.

He gets to venture into his much-loved Wales as a Welsh translator for messages Brother Mark is carrying to two newly appointed bishops.

The first message is delivered to the court of Bishop Gilbert, who is playing host to Prince Owain Gwynedd and trying to smooth the relations between Welsh royalty and the Church.

During their stay at Gilbert's court, Cadfael and Mark meet a lovely young woman, Heledd, who comes to figure prominently in the story, and Bledri ap Rhys, a messenger from Owain's rebellious brother, Cadwaladr.

Syst., Garland Copyright 2002 Reed Business Information, Inc.[17]Publishers Weekly has a terse summary: Twelfth-century monk and sleuth Brother Cadfael, making his 18th appearance, must go deep into Wales on a pilgrimage of Church diplomacy.

[19][20] Billy J Hobbs claimed this was his favourite in the series, as it brings up well Cadfael's past as a soldier, and there is suspense in whether the Danes will invade.