Warning: This article contains spoilers for Series 1, 3 and potentially Series 4 of Sherlock.

One of the most popular fan theories surrounding the upcoming season of BBC’s Sherlock just got a huge boost from an unlikely place: a coloring book.

Tumblr user ladymacphisto did the rest of the fandom a major solid this week when she decided to buy the newly released adult coloring book aimed at fans of the show. Titled Sherlock: The Mind Palace, the book is an “official” coloring book that includes “vital” clues that illustrator Mike Collins has drawn into notable scenes from the show.

While thumbing through the pages for the first time, Ladymacphisto immediately picked up on a clue to a possible series spoiler that, if true, would mean fans have been right about a major theory they’ve been arguing for years: The theory that John’s wife Mary is actually one of Sherlock’s most formidable villains, Sebastian Moran.

In the original Holmes canon, Moran is the criminal assistant to the infamous Moriarty. Though we’ve never actually seen or heard from Moran in Sherlock, his specter has loomed over the show since season 1, most notably in the “swimming pool” scene that both closes season 1 and opens season 2. In that scene, viewers realize that Moriarty has a set of very skilled snipers under his command. Canonically, marksmanship is one of Sebastian Moran’s most notable qualities, as is his past as a decorated member of the army. Both facts quickly coalesced into the theory that one of the marksman in the pool scene was Moran, and that he’s been working for Moriarty throughout the show.

Astute Sherlock fans have been arguing the “Mary Morstan = Mary Moran” theory for years, since before she actually appeared on the show in the third season. Though at first the only connection seemed to be the canonical similarities between their names, the third season gave a major boost to that theory, when we learned that Mary is actually a deadly marksman, an assassin with a mysterious past and no qualms about near-fatally shooting her husband’s best friend.

Yet at the third series’ conclusion, it seemed John and Mary had reaffirmed their love and were back together, with John destroying a file of information revealing her past without reading it; no further harm done. Right?

Not so fast. Moriarty returned at the end of the season finale, leaving us all on various cliffhangers—like wondering how he survived a gun shot point blank to the temple, and whether he’d returned to reclaim Mary, his right-hand woman.

Enter the coloring book. It handily lists for the reader which clues the artist has drawn into various scenes from the show, and which episodes they relate to. One huge clue given to us is Mary’s wedding ring, and Ladymacphisto quickly ascertained that it had shown up in the most telling scene of all: