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Sherlock Holmes certainly prides himself on never making a mistake, but he might have slipped up by accident — and in a coloring book of all places. Here’s a spoiler warning for current and future episodes of Sherlock, just in case.

If you’re completely caught up with Season 3 of Sherlock, you know that John Watson marries a lovely lady named Mary Morstan. It’s all great and awesome, except for the fact that Mary has got a lot of secrets. When Sherlock first meets her, he knows she’s hiding something. Remember this magical moment?

In the end, it turns out that Mary’s a former assassin with an excellent shot. She comes clean about it to John and Sherlock, and they decide to leave the past in the past. That hasn’t stopped the theories and speculations about her, though, and that she still might be hiding something BIG.

A popular fan theory is that Mary is actually an updated female version of Sebastian Moran, an assassin with an excellent shot in the Sherlock Holmes novels. Sebastian also happens to be employed by a Mr. James Moriarty. Going back to the end of Season 1, when Sherlock and Moriarty finally meet at the pool, Moriarty has some sharpshooters aimed right at him and John. The theory was that this shooter was Sebastian, but they were never revealed.

Now fast forward to Season 3 and suddenly there is a highly-trained shooter in the mix, with a last name kinda similar to Moran (Morstan), and it seems like too much of a coincidence, right?

How does this coloring book come into play? As Tumblr user ladymacphisto points out, there’s a clue connecting Mary and Moriarty right in the pages of the book. The totally adult coloring book Sherlock: The Mind Palace (which you can buy right here, right now) explains that while coloring, you’re also supposed to be looking for “a vital clue from each episode” in every image. The vital clue from “A Sign of Three” is Mary’s wedding ring, and it’s hidden in the pool scene… that was thought to originally connect Moriarty and Sebastian!

That can’t be a coincidence. This coloring book is also the “officialSherlock coloring book, with the BBC’s blessing. So does that mean… could it be… is this fan theory true? Is Mary really Sebastian Moran? I also do not subscribe to the belief that Moriarty is dead, because he’s totally coming back. He has to. Good thing in his absence Mary cozied up to our favorite sleuthing BFFs.

Check out ladymacphisto’s full Tumblr post here complete with lots of pictures and decide for yourself if this is true or not. And is it crazy to look for clues inside coloring books? Probably. But this is what happens during Sherlock hiatus.

(Images via BBC.)