When watching Game of Thrones it's very important to pay close attention to every last detail, because you never know when something you thought was minor is going to show up again. In Season 7, that detail is a certain dagger. What is Littlefinger's dagger on Game of Thrones? It hasn't really shown up since way back in Season 1, but it looks like this little piece of metal is about to play a big part in the action coming up.
If, like myself, you don't have an encyclopedic Game of Thrones memory, you may be wondering what this dagger actually is. The catspaw dagger, made of Valyrian steel with a dragon bone handle was used to try and assassinate Bran Stark while he was in a coma after having been pushed out the window by Jaime Lannister — strange to think this was not actually Bran's worst day. Catelyn Stark got hold of the dagger and took it to King's Landing to do some investigative work, where it found itself in the hands of Littlefinger. Lord Petyr Baelish used it to threaten Ned. And that was the last we saw of the dagger up until now, where hints of it have been dropping left and right.
It first showed up in a book Sam Tarly was reading in Oldtown in the season premiere. Sam didn't appear to recognize it, but it does confirm that the blade is Valyrian, so will presumably be an effective weapon against White Walkers. It shows up again in a preview for Episode 4. It's difficult to tell, but it certainly looks as though the person unsheathing the dagger is Littlefinger himself. But the most interesting hint that the dagger is going to be important in episodes to come is a certain Entertainment Weekly cover in which Arya is pictured with the dagger resting comfortably on her hip. It's clear that Arya is heading to Winterfell where Littlefinger is currently seducing/harassing her sister Sansa.
Jon already threatened to kill Littlefinger if he touched Sansa, but he's got a bit more self-control than his plucky assassin little sister. If Arya learns of some sort of underhanded plot of Littlefinger's, or maybe finds that he had a hand in pretty much every terrible thing that's happened to her family, I have no doubt that she'll dispatch him posthaste, and perhaps take the dagger for herself. Honestly, I really hope she does because I don't know how much more whispering from Littlefinger either Sansa or I can take.