Tonight's season premiere episode of Game of Thrones called all the way back the show's first season with a sneaky Easter egg hidden in a book in the Citadel at Oldtown.
The book in question was taken by Samwell Tarly from the restricted area of the Citadel's library. Within the book is a sketch of a very particular dagger.
The dagger in question is the one that was used by the assassin who attempted to murder Bran Stark at Winterfell. The dagger was made of dragonsteel, one of the only materials known to be capable of slaying a White Walker, which would explain why it was represented in a book of interest to Sam.
The dagger's oldest known owner was Petyr "Littlefinger" Baelish. When the dagger was used in the attempted assassination of Bran Stark, Littlefinger took advantage of his childhood friendship with Catelyn Stark. He lied to Catelyn and told her that Tyrion had won the dagger, indicating that Tyrion was the one who ordered Bran killed and thus kicking off the chain of events that would lead to the War of Five Kings.
However, the truth was that King Robert Baratheon had won the dagger from Littlfinger, not Tyrion. Later in George R.R. Martin's A Song of Ice and Fire novels both Jaime and Tyrion independently figure out that it was most likely Joffrey who took Robert's dagger, gave it to the assassin, and ordered Bran killed, either in a fit of cruelty or a misguided attempt to impress the man he believed was his father.
Whether the dagger appearing in Sam's book indicates some deeper connection between the dagger and the coming events or is just a subtle Easter egg placed there because of the dragonglass connection remains to be seen.
In the Game of Thrones seventh season premiere episode, "Dragonstone," Jon (Kit Harington) organizes the defense of the North. Cersei (Lena Headey) tries to even the odds. Daenerys (Emilia Clarke) comes home.
In Game of Thrones Season 7, Daenerys Targaryen has finally set sail for Westeros with her armies, dragons and new Hand of the Queen, Tyrion Lannister. Jon Snow has been named King in the North after defeating Ramsay Bolton in the Battle of the Bastards and returning Winterfell to House Stark. In King's Landing, Cersei Lannister has seized the Iron Throne by incinerating the High Sparrow, his followers and her rivals in the Sept of Baelor. But as old alliances fracture and new ones emerge, an army of dead men marches on the Wall, threatening to end the game of thrones forever.
Game of Thrones airs Sundays at 9 p.m. ET on HBO.