‘How about some coffee, old girl?’
Miss Vane looked at him coldly. ‘I said you could come round. If you want someone to serve you food and drink, I suggest you employ a maid.’
‘Mr Boyes!’ exclaimed Hannah Westlock, opening the door to find that gentleman on the top step, supported by the strong arm of the driver. ‘Now you sit down here, and I’ll ring for the doctor.’
‘Never mind the doctor, get me a brandy. That b- wouldn’t even give me a cup of coffee.’
Forget buying poison while giving the name of famous murderers, or living with your boyfriend. Ironically, what ultimately lands Harriet Vane in the dock isn’t a social transgression, but adherence to social rules of politeness, first that Harriet actually agree to Boyes' demand that they meet, second that having done so she is required to play the hostess. Rules so strict that the murderer can rely on them in setting up his alibi: Urquhart offers Boyes Turkish coffee, which Boyes doesn’t like, thus setting up the chance for a statement that Harriet will offer coffee, and increasing the chance of Boyes actually drinking it.