The idea was born more out of paranoia than logic. Five knows this. Karsa talking about the crew 'missing something' was probably metaphorical, or simply an insult that he wasn't supposed to read into. There is also a chance that it wasn't. With everything else out of his control, it's hard not to obsess over something when he happens to have an easy (not insane) way to find out.

He's on his way to where he thinks she's staying, but he hesitates outside the door. It would be easier just to blink inside before anyone saw him, but he's still not sure how familiar he should be around her. Their last conversation seemed amicable enough that he's considering this. And it's potentially important that he follow up on his hunch if it means getting them ahead of any horrible curse that they're sailing into.

"Winnie. Are you in?" He looks to either side of him and rocks back on his heels with his hands in his pockets. They're... good now. He's sure this won't be a big deal. "I have something I need to run by you."