After his conversion to Roman Catholicism in 1914, Mackenzie explored religious themes in a trilogy of novels, The Altar Steps (1922), The Parson's Progress (1923) and The Heavenly Ladder (1924).

[8] In 1922, Robin Legge, chief music critic of The Daily Telegraph, encouraged Mackenzie to write some of the earliest gramophone record reviews.

His ill-health making front-line service impractical, he was assigned counter-espionage work during the Gallipoli campaign,[12] and in 1916 built up a considerable counter-intelligence network in Athens, Greece then being neutral.

[13] He is alleged to have taken part in an attempt to assassinate the King by poison in August 1916, during which the royal palace was to be surrounded by fire to prevent him escaping.

[14] While his secret service work seems to have been valued highly by his superiors, including Sir Mansfield Smith-Cumming, his passionate political views, especially his support for the Venizelists, made him a controversial figure and he was expelled from Athens following the Noemvriana.

Smith-Cumming considered appointing him as his deputy, but withdrew the suggestion after opposition from within his own service, and Mackenzie played no further active role in the war.

Mackenzie states that a plea-bargain (described in the text as "an arrangement") had been reached with the judge prior to the trial: in exchange for his pleading guilty, he would be fined £500 with £500 costs.

However Sir Thomas Inskip, then attorney general who prosecuted the case, succeeded in annoying the trial judge to such an extent that he then reduced the penalties to a token amount.

Even so, the costs of his defence and the withdrawal from sale of Greek Memories left Mackenzie out of pocket and an attempt was made to ask the authorities exactly which passages in the book they objected to so it could be re-issued with the offending material removed.

[17] In Octave Eight, covering the years 1939–45, Mackenzie recounts that the matter was raised in Parliament and a new version of Greek Memories was eventually published in 1939.

[21] In 2011 Biteback published the original 1932 edition of Greek Memories, including the Secret Intelligence Service memo detailing the offending passages of the book.

[24] According to a 1938 Time article Mackenzie had intended to write a book in support of Edward but abandoned the plan when the Duke asked him not to publish.

Compton Mackenzie's observations on the local life of the Italian islanders and foreign residents led to at least two novels, Vestal Fire (1927) and Extraordinary Women (1928).

The latter, a roman à clef about a group of lesbians arriving on the island of Sirene, a fictional version of Capri,[27][28] was published in Britain in the same year as two other ground-breaking novels with lesbian themes, Virginia Woolf's love letter to Vita Sackville-West, Orlando, and Radclyffe Hall's controversial polemic, The Well of Loneliness, but Mackenzie's satire did not attract legal attention.

[30] Mackenzie went to great lengths to trace the steps of his ancestors back to his spiritual home in the Highlands, and displayed a deep and tenacious attachment to Gaelic culture throughout his long and very colourful life.

Although from the north east of England, he "was influenced in the choice of Albion as 'my' team by the fact that their ground was romantically called The Hawthorns and that they were nicknamed the Throstles".

[41] Mackenzie died on 30 November 1972, aged 89, in Edinburgh and was interred in St Barr's churchyard cemetery at Eoligarry on the Isle of Barra.