OK, let's re-imagine this novel in the style of Stone's Fall. Actually, Lawton himself used a very similar method in Old Flames. Fictional Inspector Troy met historical Nikita Khrushchev during his 1956 visit to Britain and had some interesting conversations.
In case you haven't read Stone's Fall, author David Liss created an ingenious fictional alternative to the recorded historical events surrounding what came to be known as the Panic of 1890 (expertly described by historian Philip Ziegler in The Sixth Great Power: A History of One of the Greatest of All Banking Families, the House of Barings, 1762-1929).
Lawton, in a way, did the same thing. His alternative asks, "what if Ward's death was murder - not suicide?". He also, however, wanted to weave in some of Troy's history and associates from other novels. One advantage to replacing the main historical characters with similar-but-not-identical fictional creations is that the Inspector Troy-style story is less constrained by the historical story. For instance, it's hard to imagine that a murder committed by a Scotland Yard detective could have gone unreported in the press, so the fictional Detective Inspector Blood replaces the actual Scotland Yard vice investigator involved in the Ward case (Lawton notes that the history of real detective Harold Challenor was a partial inspiration for the Blood character). Also, one of the fun things about the Troy novels is the way familiar characters keep showing up in unexpected ways. A Stone's Fall approach would not have given Lawton such latitude. Still, for a reader who, like myself, enjoys the history in historical fiction, there's something unsettling about Lawton's blurring of the lines between the two. I think I prefer Blackout or Old Flames to A little White Death.