One possible fanfiction could involve Snape getting injured by a spell gone wrong during an Order meeting. Maybe a new member accidentally casts a hex in his direction. His injury could then lead to a series of events where the Order has to figure out if it was truly an accident or a sign of a spy within their ranks.
The plot could be that Snape is injured by a dark magic artifact that was being examined at the Order meeting. This injury could make him vulnerable and force him to rely on others, which is a big change for his character. It could also create a rift in the Order as some believe he brought the danger upon himself.
In some fanfictions, Snape's injury at the Order meeting could be a catalyst for character relationships. For example, it could bring out a more protective side in Harry. He might start to see Snape in a new light, not just as the strict teacher but as a vulnerable ally. This could then lead to a whole new dynamic between them and other members of the Order.
In a Snape Order meeting in fanfiction, there could be intense discussions about the fight against Voldemort. Snape might share some crucial information he's gathered from the Death Eaters. Members of the Order could be suspicious of him at first, but as the meeting progresses, they start to see his value in the fight.
Obviously, Snape himself would be a key participant. Then there could be Lupin, as he's an important member of the Order. McGonagall might also be there, representing Hogwarts. And perhaps Moody, with his expertise in fighting the Dark Arts.
One common theme is secrecy. Snape's double - agent status means there's always an air of mystery during Order meetings in the fanfics. Another is tension, as members may or may not trust him.
He could be suspected by Voldemort. Since Voldemort is very paranoid, an injury at a meeting might make him think Snape is up to something or being careless in a way that could endanger their plans.
Well, there's a fanfic called 'Snape and the Unusual Order Meeting'. It delves into the tense atmosphere when Snape is suspected by some members during an Order meeting. The interactions between Snape and other characters like Sirius are really interesting to read. There's also 'Snape's Role in the Order Meeting Crisis' which focuses on how Snape uses his intelligence to solve a problem that arises during a crucial Order meeting.
In some darker fanfictions, it could be a member of the Order who has always suspected Snape of being a double agent. This person might have decided to take matters into their own hands and attack Snape during the meeting, believing they are protecting the Order from a potential threat.
One interesting Snape - injured fanfiction is 'The Wounded Professor' on FanFiction.net. It details his recovery after a particularly nasty hex from a mysterious assailant.