He was recalled in February 1917, being close to retirement age and due to some uneasiness in Whitehall that he had not promptly reported a peace feeler by the German Imperial Chancellor, Theobald von Bethmann Hollweg.

When the hero (who is no less a person than the Duke de Richleau) escapes from Germany to neutral Holland with important information for the British Government, Johnstone, as His Britannic Majesty's Envoy to the Netherlands, plays a key part in springing him from jail, helping him dodge German agents and generally getting on his way.

Though The Second Seal is a work of fiction, it is heavily based on fact, including the following bits of information about Johnstone: " [Johnstone] held the belief that his duty lay in keeping a good and hospitable table in the country where he was stationed, and arranging for its notables to engage in golf tournaments with their British equivalents; and if he did that, the negotiation of rather dreary affairs, such as trade pacts, would prove a simple matter for those who understood them better than he did.

The success of his missions proved that there was much to be said for this policy..."When the hero reaches the safety of the British Legation at The Hague, Johnstone offers him some excellent brandy.

"Wheatley had earlier used this 'medicine' trick of Johnstone's in his 1936 thriller Contraband, attributing it to his well-connected character Sir Pellinore Gwaine-Cust (Chapter XXI).