I found this fairly fast-paced, having gotten used to some of Ferguson's other stories, which seem to drag horribly in the middle. This one was mercifully short at 222 Kindle pages. Mild spoilers follow.
Written after 1918, this is a sort of Boy's Own adventure story, set in the innocent time before WWI, when the Germans were acting friendly to Britain on their face, but plotting conquest behind their backs. A Scottish doctor studying in Berlin comes across a packet with a paper inside under very disturbing circumstances, and is chased around by deadly enemies who want to retrieve it. He has adventures getting out of Germany and back to Scotland, where he thinks himself safe at his remote Scottish home. He is found, however, and leads them on a merry chase away from his mother's house to London and then the Kentish coast. for the exciting conclusion. A young woman also gets involved. This would have made a good early Hitchcock film, in the vein of The 39 Steps.
As so many of Ferguson's stories seem to do, the plot turns on a mysterious paper which, when he finally is able to open it, turns out to be a childish drawing. What this drawing means is not immediately clear, and even when he has figured out some of it, he can't get anyone to believe it is anything more significant than it appears, until ... well, I'll leave that for you to discover.
A decent thriller very much in the tradition of John Buchan's The Thirty-Nine Steps.
In the Berlin of 1914 a dying man hands over a package to our everyman hero, a medical student from Scotland called Abercromby, a difficult name for the baddies to get right although I was disappointed that amongst all their mispronuciations no-one thought to call him Apllecrumbly.
From this moment on he will be hunted from Berlin to Hamburg and then from Scotland, where he is chased through the heater of Kincaidshire, down to London and finaly the Kentish coast where the roles of hunter and hunted are reversed.
There is the usual conspiracy of German spies with agents everywhere, the Macguffin in this instance looks like a child's drawing but is in fact...well, it doesn't matter what it really is of course.
Fortunately for Aplleturnover he has the assistance of Margarita Thompson, a plucky heroine who helps him along the way, as well as a few random Scotsmen who turn up in all sorts of places. There is the usual powerful super-villain to contend a knack for impersonations.
Not up to the standard of Buchan but not bad by any means.