Innes put pen to paper in order to supplement his income and wrote, in only six weeks, Death at the President's Lodging, which was published in 1936. Whilst he wrote later under his own name, J.I.M. Stewart, it is for his work under the Innes pseudonym for which he is best known.
His main series character was John Appleby (later Sir John) who first appeared in Death at the President's Lodging which was re-titled Seven Suspects for its publication in the USA. Appleby was a well-educated and erudite character frequently given to literary flourishes and quotations. The first four books are probably the best and are important in the crime fiction genre.
Innes has a colourful and urbane writing style which is, unusually in this field, weighted towards dialogue, verbal exchanges and well rounded characters rather than the usual plot-driven whodunnit.

His output was certainly prodigious, writing 45 novels in 50 years as well as short stories and work under his own name. Sadly, Innes' books were, as many others, blighted by the dreaded 'Gollancz yellow jacket', a matter of some dismay to collectors and presumably authors alike. It is fair to say that most of his best work is to be found amongst his pre-1960 titles, although the standard was always high and all his work merits attention. Innes succeeded, with Appleby, in creating a fresh, new and non-stereotypical character which secures his place as an important author in the detective fiction genre.

Some have said of Innes that his writing is over-indulgent. Whilst there are perhaps grounds for this view, his style is, for those willing to give it the time it deserves, thoroughly enjoyable.