the "little" arises from my interpretation of "mochardes" (as opposed to simply "moches"

...or simply "nasty little dealings".

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Note added at 34 mins (2021-07-29 14:53:40 GMT)
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or "nasty little goings-on"

I could not decide between these two, as I am unsure which nuance fits better, so I have suggested both as a choice - Sneaky or shady "goings-on"....!


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Note added at 45 mins (2021-07-29 15:04:10 GMT)
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Typo... Second suggestion should also be "goingS-on"...

NB: 'affaires' -> 'events' or 'incidents'.

I think, maybe, we have to look at the intended meaning here as projected through the moral values of the Agatha Christie characters (at least as perceived by the writer of the ST). In other words, things which are mochard may be so perceived according to their outlooks.

Affaires mochardes could thus be things which are unacceptable in their value systems, so it might include unwanted pregnancies, homosexuality or even incest (if such things are alluded to in Christie's works...).

"Shady" or "sleazy" things are slightly different, it seems to me: if we choose such words we are assuming that the word mochard is being applied from our value perspective, or at least that of the writer of the ST, who is probably expecting us to share her/his outlook. Which may be the case, however.

I can't decide, partly because I can't quite gauge the connotations of mochard, which is a word I have never come across... to me it may have a whiff of irony about it, which may support my view.

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Note added at 1 hr (2021-07-29 16:07:42 GMT)
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To state the obvious, perhaps, the irony seems to me to come precisely from the fact that it is essentially a "made up" word: moche + -ard: it is a word we are not meant to take seriously, suggesting that the people who are perceiving things thus are being mocked.

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Note added at 3 hrs (2021-07-29 18:00:55 GMT)
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However, the irony of mochard could also work another way: the author of the ST could be mocking Agatha Christie, her writing style, her values, rather than her characters and their values. This wouldn't invalidate my solution IMHO.

On balance I'd come marginally down on the side of the characters being mocked, as the author appears probably to rate Christie's novels quite highly.