on the memorable night of Manuel's treachery

on the memorable night of Manuel's treachery
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on the night of the commemoration day of Manuel's treachery (the day when Manuel - the Byzantine emperor was betrayed)?

Context:

The Judge was at a meeting of the Raisin Growers' Association, and the boys were busy organizing an athletic club, on the memorable night of Manuel's treachery. No one saw him and Buck go off through the orchard on what Buck imagined was merely a stroll. And with the exception of a solitary man, no one saw them arrive at the little flag station known as College Park. This man talked with Manuel, and money chinked between them.

More:

http://london.sonoma.edu/Writings/CallOfTheWild/chapter1.html