Lord Peter is introduced as nervy, edgy and insightful. Frustrated and bored, definitely suffering from shell shock. He needs an occupation to distract him from the nightmares - being a private detective, fulfils his wants although the conclusion is something he would prefer to avoid.
Bunter, the near perfect butler - too perfect sometimes? Discreet and no doubt pleased to be given such a secure position in a world burdened with unemployed ex-soldiers. He is allowed to develop his own interests and Wimsey is interested in him up to a point.
I nearly always prefer the detective stories written at the time in which they were set at the authors get the details of attitudes, morals and mores right. This sometimes leads to characters expressing inappropriate sentiments, but there should surely be a case for accepting these attitudes for what they were: the contemporary depiction of society - if all the characters had been without these opinions then they would not be of that time and background. It is interesting to see that there are subtleties of opinion where personal knowledge is reflected in the adjustment of these attitudes and opinions.
This is well worth reading if you enjoy detective fiction written and set in the early 1920s, that is mostly concerned with the upper echelons of society. It is very well written by an intelligent author who assumes her readers are her equals and is long enough to become really absorbed, but not too long.
You probably guessed - my favourite author.