Question: Which 1985 novel was set in medieval England and featured four distinct royal houses?

Context articles: Here Be Dragons
Multifocal plane microscopy
The Matter of Araby in Medieval England
Martín de Goiti
Anthony Tuck
House of Plantagenet
Jeremy Goldberg
Powell (surname)
Return of writs
Cultural regions of Latvia

Here Be Dragons is a historical novel written by Sharon Kay Penman published in 1985.
 The novel is the first in a trilogy known as the Welsh Princes series set in medieval England, Wales and France that feature the Plantagenet kings.
 Penman is known for providing accurate descriptions of historical events and creating strong characterisations.
Multifocal plane microscopy (MUM) or Multiplane microscopy or Biplane microscopy is a form of light microscopy that allows the tracking of the 3D dynamics in live cells at high temporal and spatial resolution by simultaneously imaging different focal planes within the specimen.
 In this methodology, the light collected from the sample by an infinity-corrected objective lens is split into two paths.
 In each path the split light is focused onto a detector which is placed at a specific calibrated distance from the tube lens.
 In this way, each detector images a distinct plane within the sample.
 The first developed MUM setup was capable of imaging two distinct planes within the sample.
 However, the setup can be modified to image more than two planes by further splitting the light in each light path and focusing it onto detectors placed at specific calibrated distances.
 Another technique called multifocus microscopy (MFM) uses diffractive Fourier optics to image up to 25 focal planes.
 Presently, MUM setups are implemented that can image up to four distinct planes.
The Matter of Araby in Medieval England is a 1977 book by Dorothee Metlitzki in which the author attempts to show the beginnings of the relationship between medieval England and the Arab world.
 It is considered to be the “definitive work on the intersection of Arabic and English culture in the Middle Ages”.
Martín de Goiti (c. 1534 - 1575) was one of the soldiers who accompanied the Spanish colonization of the East Indies and the Pacific, in 1565.
 From his main base in Mexico City, he was the leader of the expedition to Manila, ordered by Miguel López de Legazpi in 1569.
 There, he fought a number of battles against the Muslim, Tariq Suleiman/Soliman (Arabic سليمان), the Hindu Rajah Matanda (Hindi ऋअज ंअतन्द), and the Taoist Lakan Dula (trad.
 Chinese 王 杜拉) of the kingdoms in Luzon; for control of the lands and its settlements.
 He is also known for his statesmanship by betrothing his sister to Batang Dula, the eldest son and successor apparent of Lakan Dula of Tondo (trad.
 Chinese"東都" pronounced Dongdu), the paramount ruler of Manila.
 Eventually their descendants unified the 3 royal houses of Tariq Suleiman, Rajah Matanda and Lakan Dula with the Basque Goiti family.
 The Dula y Goiti family eventually married with the Mendoza family who came over from Latin-America, who were Sephardic Hebrews that were practicing Catholics.
 Afterwards, the Dula y Goiti surname was shortened to Dulay.
 However, during the Spanish era, some descendants changed their surnames even further in order to avoid persecution and among which; the Salonga and Macapagal families are known descendants of these royal houses albeit only through a different family name.
Anthony Tuck (born 1940) is Emeritus Professor of Medieval History at the University of Bristol.
 He was educated at the Royal Grammar School, Newcastle (1948–59) and at the University of Cambridge.
 From 1965 to 1978 he was Senior Lecturer in Medieval History at Lancaster University.
 He was also Master of Collingwood College at the University of Durham from 1978 to 1985.
 His published work focus on the relationship between the king and nobility in late medieval England.
The House of Plantagenet ( ) was a royal house which originated from the lands of Anjou in France.
 The name Plantagenet is used by modern historians to identify four distinct royal houses – the Angevins who were also Counts of Anjou, the main body of the Plantagenets following the loss of Anjou, and the houses of Lancaster and York, the Plantagenets' two cadet branches.
 The family held the English throne from 1154, with the accession of Henry II, until 1485, when Richard III died.
Peter Jeremy Piers Goldberg (born 1958) is an English historian.
 He is Reader in Medieval History at the University of York.
 Goldberg was educated at the University of York and at the University of Cambridge.
 His main interest lies within the social and cultural history of late medieval England, in particular women's and gender history.
 Among his published books are "Women, Work and Life Cycle in a Medieval Economy" (1992), "Women in England c. 1275-1525: Documentary Sources" (1995) and "Medieval England: A Social History 1250-1550" (2004).
 He has also edited several books, including "Women in Medieval English Society" (1997) and "Richard Scrope: Archbishop, Rebel, Martyr" (2007).
Powell is a surname of Welsh origin.
 It is a patronymic form of the Welsh name hywel (later anglicized as Howell), and the prefix "ap" meaning "son of", together forming ap Hywel, or "son of Hywel".
 It is an uncommon name among those of Welsh ancestry.
 It originates in a dynasty of kings in Wales, and Brittany in the 9th and 10th century, and three Welsh royal houses of that time onwards.
 The House of Tudor one of the Royal houses of England, also descended from them.
 See also: Howell (surname), and Welsh surnames.
The privilege of return of writs, in medieval England, was a right given to certain liberties or franchises to execute royal writs within the land in question.
 This in effect meant overpassing the authority normally held by the sheriff as the king's representative in the localities.
 Examples of such liberties in medieval England include the palatine counties (see county palatine) County Durham, Cheshire and the Duchy of Lancaster.
Cultural regions of Latvia are several areas within Latvia formally recognised as distinct from the rest of the country.
 While some of these regions are seen purely as culturally distinct, others have historically been parts of different countries and have been used to divide the country for administrative and other purposes.
 The Constitution of Latvia recognises four distinct regions: Kurzeme, Zemgale, Latgale and Vidzeme.