The preface is dedicated to Walter Scott, and, indeed, the narrative is very much in the vein of the Waverley novels. The story commences in Holland in the company of a regiment of Scottish campaigners fighting in the War of the Spanish Succession. At the head of the regiment is Major Ducholly, assisted by his old companion, Sergeant John Lomm. The regiment are also accompanied by the fractious Dutch man Donatus Groendyke. While on the march, they apprehend an enemy soldier and his lady, but are given the slip. Ducholly deigns not to shoot them as they flee, following the advice of John.
The narrative then travels back in time to when Ducholly was Alaster, Laird of Kempencairn (and John was his faithful servant). Shortly after the birth of his daughter, she and his wife are abducted. Overwhelmed by grief, Alaster joins the army. His foe, Crowbardy seizes his property as a result of Alaster's outstanding debts.
Back in the present, the regiment do battle with the French. Ducholly wants to die, but is unsuccessful. He bests lets Duplessis, a French count and renowned soldier, but lets him live, albeit with a few wounds. We are then introduced to Miriam Groendyke, a young woman of mysterious Scottish birth, who was raised by the Groendykes (Donatus' parents). Donatus persistently seeks her hand in marriage, but Miriam is disgusted by him. It transpires that he is a traitor to his country. Miriam is engaged to the dashing Frenchman, Jule, who rescues her when Donatus pursues her aggressively.
After the battle, John Lomm is arrested for treason, following a false accusation from Donatus. Ducholly is also accused, but he is not present, and is presumed dead. Until such time as his innocence can be ascertained, John is kept in confinement. Shortly afterwards, he is released and is enlisted by Duplessis to help find Miriam, which he does and becomes her protector.
Later, after John has been separated from Miriam, she meets Ducholly. He realises that she was the lady who accompanied the enemy soldier. Although somewhat worse for wear, Ducholly rejoins his regiment and leads them against the French. While this is taking place, Donatus tries to capture John, but Duplessis helps him to escape. By chance, Donatus discovers Miriam, and tells him that Jule is dead, which sends her insane. Donatus abducts her, but accidentally reveals that she is of the house of Kempencairn. At that moment Ducholly walks in. He and Miriam are briefly reconciled, only for Donatus to overpower Ducholly. John and Duplessis fortuitously run in at that moment and defeat Donatus. Duplessis, we learn, was Miriam's paramour Jule all along. The circumstances of Miriam's parentage are then clarified: Donatus was the one who abducted Ducholly's wife and child (Miriam). After the wife died, Donatus turned his attentions to the daughter.
Later on, Ducholly dies of old age. Duplessis and Miriam marry, and, with John, return briefly to Kempencairn which is in ruins. They are warmly welcomed by the locals nevertheless.

'Tournay' features extensive representation of Scots dialect, particularly in the speech of the soldiers of Ducholly's regiment. John Lomm has the most speaking parts, and his utterances contain marked Scots vocabulary items, respellings and grammar. The novel also includes some interesting metalanguage concerning Ducholly's accent (the only thing that outwardly connects him to Scotland) and Miriam's familiarity with the language of Scotland. The final chapter of the novel, which follows Miriam and Duplessis back to Kempencairn, includes some dialect representation in the speech of the locals.

Unexpectedly nondialectal characters: The narrator mentions that Ducholly has a Scots accent, but no dialect representation is included in his direct speech.