Lord Peter, however, proves that Mary was lying to protect her secret lover Goyles, with whom she had been planning to elope on the night of Cathcart's death.
He has meanwhile invited Lady Mary to dinner several times but is nervous of making their relationship public, in spite of Wimsey's encouragement.
In Strong Poison, Parker has apparently made a good case against mystery writer Harriet Vane for the murder of her former lover Philip Boyes.
The Duke and Duchess of Denver are shocked by the match, but Wimsey insists that "one of these days he'll be a big man, with a title, I shouldn't wonder, and everything handsome about him."
In Five Red Herrings,[5] Parker assists the Dumfriesshire constabulary by easily tracing a suspect who has fled to London in disguise (although he proves to be innocent).
In The Nine Tailors, Parker once again assists a county police force, this time the Lincolnshire Constabulary, in Wimsey's investigation into the case of an unlawfully buried body.
Parker uses questionable tactics when he places a hidden microphone in the interview room where they are waiting (or in the TV adaptation, leaves a desk intercom "live").
Parker does not feature in Gaudy Night, and appears only very briefly at the wedding of Wimsey and Harriet Vane in Busman's Honeymoon.
The Duchess of Denver is snobbishly opposed to that match too, and writes to a friend, "Mary's policeman was bad enough, but he is at any rate quiet and well-behaved..." In A Presumption of Death, the World War II Wimsey novel by Jill Paton Walsh, Harriet takes the three children of Charles and Mary to Talboys, together with her own children – both to keep them safe from bombed London and to free their parents to help the war effort.
As depicted here, Wimsey was a shell-shocked World War I veteran who accidentally discovered in himself a talent for detection when present in the house of another aristocratic family when emerald heirlooms mysteriously disappeared.
He was born or raised in Barrow in Furness, a steelworks town created in the 19th century Industrial Revolution, which tends to increase the contrast between his origins and those of the aristocratic Wimsey.
In Clouds of Witness it is noted that Parker is not usually given to sudden bright flashes of insight or spectacular displays of happy guesswork, which are "more in Wimsey's line".
When a maidservant in the household of a wealthy lady remarks (in The Unpleasantness at the Bellona Club) that Parker appears to be "Quite the gentleman", the cook rebukes her, saying "No Nellie; gentlemanlike I will not deny; but a policeman is a person and I will trouble you to remember it."
When involved in such investigation on a hot London day, Parker – grabbing a hasty snack at a sleazy restaurant – feels rather resentful when thinking of Wimsey at the same time eating at his club.