Poor Daisy Dalrymple is having trouble with a tooth, so she makes an appointment to see a local dentist. When she arrives for her appointment though the dentist as first can't be found, and when he eventually is he is in his dental chair, with a mask feeding him Nitrous Oxide, which has killed him. With the household believing it to be an accident, Daisy isn't so sure, neither is her husband, when he is called in.
With a nurse and lady's servant arguing all the time, the dentist and his wife both having affairs, and another person dying, there is a lot for the police to be getting on with, and even if they do get the right person, do they have enough evidence?
This is a good story to relax with, but the mystery part of it was really quite easy to work out, although reading about the police trying to get evidence and chasing down alibis does make this an absorbing read.