In "Beyond the Wall," he's successfully pitted the Stark women against one another by drawing on their worst instincts. Arya wants to know why her father had to die -- a question with no answer. Sansa wonders whether her sister is unhinged (and a few extra whispers from Littlefinger only fan the flame). But as soon as Arya hands Sansa the dagger, we know he screwed up. Like many, Varys underestimated the Stark women, if he knew them at all. It's time to bet against Littlefinger.
The above video recaps the path of Arya's dagger, but here's the briefing: In Season 1, someone hired an assassin, wielding this Valyrian steel blade, to kill Bran Stark. Littlefinger eventually tells Catelyn Stark that the blade is his, though he lost it to Tyrion in a bet, leading the Lady of Winterfell to go for the Lannister man's neck. Littlefinger manages to snag the dagger off Ned Stark's desk in the fourth episode of Season 1, and it's only cropped up again this year, gifted to Bran as a creepy memento of his fallen mother. Yeah, right.