Innes’ book, written in the early years of WWII, was on the NYT 125th Anniversary issue’s list of the 13 best mysteries of the last century, and though quite dated, it’s easy to see how it made the list.

Innes’s primary character is Inspector John Appleby of Scotland Yard and his good friend, the archeologist from the British Museum, Ambrose Hetherton.  They find themselves in the middle of a complicated string of events while investigating the murder of a seemingly innocent, boring, and unobtrusive poet named Philip Ploss.  Along the way we meet Sheila Grant, David Evans and a host of other interesting characters all tangled up with the eponymous secret vanguard, a group of Nazi spies who have infiltrated Scotland in an attempt to steal Professor Orchard’s formula for a truth serum.  Totally ridiculous story, but written with skill that keeps one turning the pages to see what the next twist in the plot will be.

Innis, one of the masters of the British mystery along with Christie and Sayers, , wrote under a pseudonym.  His real name is J.I.M Stewart and besides the 50 mysteries he wrote, he was an Oxford professor who wrote literary criticism including books about Joyce, Kipling, and Hardy.  Have to love those intellectual Brits!