Question: What was the George Mackie Watson RIBA's masterpiece about?

Context paragraphs:
Marauder Cars: Marauder Cars was a British car company founded by Rover engineers George Mackie and Peter Wilks.  The pair left the Rover Company in 1950 to form Wilks, Mackie and Company to exploit their idea of a two-seater sports car (the Marauder) based on the new Rover 75 chassis.  Manufacturing started in Dorridge, West Midlands and later in Kenilworth, Warwickshire between 1950 and 1952.  In 1951, the company name was changed to the Marauder Car Company.

George Somers Leigh Clarke: George Somers Clarke (1822–1882) was an English architect.  He became a RIBA Associate in March 1845 and a Fellow in June 1859.  He sat on RIBA Council.  In 1868 he had offices at 20 Cockspur Street, London.  He was a pupil of Sir Charles Barry and worked for him on designs for the Palace of Westminster in 1849.

Eilean Donan: Eilean Donan (Scottish Gaelic: "Eilean Donnain" ) is a small tidal island where three sea lochs meet, Loch Duich, Loch Long and Loch Alsh, in the western Highlands of Scotland.  A picturesque castle that frequently appears in photographs, film and television dominates the island, which lies about 1 km from the village of Dornie.  Since the castle's restoration in the early 20th century, a footbridge has connected the island to the mainland.

George Mackie Watson: George Mackie Watson RIBA (1860-1948) was a Scottish architect in the late 19th and early 20th centuries.  His masterpiece is the total rebuilding of Eilean Donan 1912-1914.

List of Sunderland A.F.C. managers: Sunderland Association Football Club was founded in 1879.  After turning professional in 1886, the club appointed Tom Watson as their first manager, and under Watson the team won the Football League First Division three times in four seasons.  The percentage of games won under Watson remains the highest of all time for a Sunderland manager.  Watson left to manage Liverpool and was replaced by Robert Campbell, but the new manager failed to continue the success of his predecessor.  The next three managers, Alex Mackie, Bob Kyle and Johnny Cochrane, each won the First Division title while at the club.  Kyle's 817 games in charge, spread over 19 full seasons either side of the First World War, make him Sunderland's longest-serving manager.  Cochrane led the club to their first FA Cup victory, beating Preston North End 3–1 in the 1937 final.  The closest they had come in previous seasons was as losing finalists in 1913 under Kyle.

Ionia (Trevilians, Virginia): Ionia is a frame house near Trevilians, Virginia, that was the centerpiece of a large plantation in the late 18th and early 19th centuries.  Built around 1775, Ionia was the home of the Watson family.  It was built as Clover Plains by Major James Watson, the son of a Scottish immigrant, in a fertile area of Louisa County, Virginia that is now a National Historic Landmark District, the Green Springs National Historic Landmark District.  The plantation was the third largest in Louisa County in the late 18th century, leading to the nickname "Wheat Stacks" for Watson as a result of his prosperity.  After Major Watson's death in 1845 the house passed to his son, Dr. George Watson, who renamed the house "Ionia" and, since he lived in Richmond, used it as a summer residence.  George Watson died in 1854, leaving Ionia to his widow, who lived there until the 1870s.  Following her death in 1879 the property was subdivided.  The Watson family went on to build a number of houses in the Green Springs area.

George Mackie, Baron Mackie of Benshie: George Yull Mackie, Baron Mackie of Benshie CBE DSO DFC (10 July 1919 – 17 February 2015) was a Scottish Liberal Party politician.

Edward George Bruton: Edward George Bruton (17 February 1826 – 3 August 1899) was a British Gothic Revival architect who practised in Oxford.  He was made an Associate of the Royal Institute of British Architects (RIBA) in 1855 and a Fellow of the RIBA in 1861.

George Mackie (footballer): George Mackie (born 18 May 1954) is a Scottish former professional footballer who played as a defender and midfielder.

John Mackie (footballer, born 1976): John George Mackie (born 5 July 1976 in London) is a former professional footballer who is best known for his time at Reading F.C. and Leyton Orient Mackie was a central defender.

Supporting paragraphs: George Mackie Watson Eilean Donan
Answer: a small tidal island