Alternatively: You tell me. This is likely the first adventure in your campaign, so just tell your players to explain to you why they want to compete in the Market Games as character creation and frame it as This Is How You Met.
If you want to flesh things out a bit, go grab Call of the Netherdeep, grab all the festival games, and plop 'em down in the Night Market.
So then, games proceeding apace, you bring in the marketplace sabotage and trigger an investigation. This is your B-plot instead of your A-plot and it's no longer locked behind the Market Games.
This is actually pretty easy to achieve: Just read through the adventure and every place where it says "if the PCs do X, they don't find anything" replace it with "if the PCs do X, they find [useful information]" and you'll ironically end up with a pretty robust mystery.
The two key revelations I'd focus on would be: 1. Persimmons are associated with the mischief sites. (And you can then trace the persimmons to Aroon.) 2. There's some sort of invisible, flying blue monkeys. (And then you can catch + interrogate them or follow them to Aroon.)
Standard three clues for each. Either gives you multiple paths to ultimate success. (PCs can even combine the revelations by, e.g. using persimmons to set a trap for the wynlings.)
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