As we know from the series, Wooster is a British spy, working in the service of Her Brittanic Majesty Elizabeth. (At least, I'm asserting that it's Elizabeth.) The interesting question is, what does Sleipnir know and think about all this?
She ought to have an inkling about what's going on with him. Probably at some point he tried to sound her out on the subject of British loyalties, to figure out whether she would be a good ally. She didn't give the answers he wanted, so he backed off on it, but it left her thinking about where his loyalties actually lay. She may even have mentioned this to Gil, eventually resulting in him finding out about Wooster's true status.
In fact, her feelings are mixed -- she's Irish, so that's natural. Her family was a longtime ally of Elizabeth's, but has been forcibly allied with Klaus for the past decade, not least because of her position as a hostage, so they've had no choice but serve him. But really, she dislikes both sides: her house has so long served as a pawn in the greater game, that a part of her would be happy to have both of them fall. Yet, she is sensitive enough to the danger of chaos that she knows this is untenable.
So she starts out fairly sure that Wooster is a spy, and she's tempted to help him, especially if he will help her escape. But she genuinely likes Gil, and doesn't want him hurt in the course of things, so she needs to know that Wooster isn't a danger to him.
This plot needs to be cross-indexed with Suspected Revenant, which calls for Wooster to have done a little bit of subtle sabotage in past months.
Characters In Game: Sleipnir Wooster
All Characters: Sleipnir Wooster