It would have to be the current plot happening at Up In The Air. I can't give too much details but it spans from a simple Tunnelsnake Infestation and directly affected the first IC hatching at Telgar Weyr.
In our cannon, Benden has fallen from top; they are no longer the leaders of Pern. A fatal fight against a new type of Thread, dubbed Immortal Thread, two turns previous, has left them roughly 250 dragons strong. Most Weyrs are holding 350-600 riders in their population, except Benden. They fought against the Immortal Thread as a Weyr and lost all of their able, mature dragons. One Wing survived but died due to a poison the Immortal Thread emits when falling. So they were extremely weak and the other Weyrs sent as many able riders as they could and Telgar even sent Vermeil Veyrilapth to clutch fresh eggs for them.
Now that they are getting stronger, they are looking to take back the glory of being the Leading Weyr. So they sent out the Tunnelsnakes systematically so that they could switch dud eggs with viable eggs from Telgar, High Reaches, and Fort. They waited for the moment the clutch mothers' left the sands to help their riders fight the 'snakes.
At the Hatching, a Gold hatched that wasn't supposed to be in a Vermeil's clutch. All the dragonriders knew something was amiss, but Clytie of Vermeil Veyrilpath has the only piece of evidence: A Bronzerider's shoulder knots ripped off from when they switched the eggs.
There's more to come. But it has yet to happen IC so I can't dive any more into it. But this plot is extensive and I'm extremely proud over it. My moderators are amazing at helping create plots as well.