How do the puzzle pieces fit together? Like putting together a jigsaw puzzle, unraveling a mystery story involves finding the ways the nubs and gaps line up, and in many cases, we find ourselves starting with the frame and working inward. In the case of Kei Sanbe's The 13th Footprint, we have the center – the upcoming fatal fire at the family home – and now have gone back and are putting the frame together. The real mystery is what fills in the space between.

As with the first volume, the postcards Touya has been receiving are a major element. When volume one ended, Ao had found the next postcard in the hidden attic, and because there was no other plausible explanation, he assumed his father put it there as part of a real-life RPG modeled on his favorite video game. Ao thinks it's a quest for him to embark upon, and he drops several hints to that effect to his parents, who are just confused. It isn't until later, when he realizes that he hasn't gotten another postcard, that Touya puts things together.

Ao's misadventure also forces him to look more closely at the cards themselves. When his son says that he believed his dad wrote the note because of the way the number on the front was written, Touya has the sudden, horrible realization that it is his handwriting on the front – and these were, at one point, his postcards, a set of ten featuring places he dreamed of visiting as a child. (You may recall that the burnt card in the debris in the series' opening pages has the number ten on it.) But Touya also recalls giving his cards away to a friend back in elementary school – a friend who was only around for a few weeks before vanishing.

Given that this is by the creator of Erased and For the Kid I Saw in My Dreams, the disappearance of a child should make readers sit up and take note. Sanbe has a history of writing about vanished (and abused) children, so the fact that Touya's friend disappeared isn't something we should just brush off. Touya, at first, believes the friend was imaginary based on his loneliness, but Haru later mentions that she saw them, too. So if the answer isn't supernatural (and I really don't think it is), then what's left is a much scarier possibility: that the friend was taken or forced to move. There's a lot that doesn't quite add up about them, even beyond Touya's suspicion that they weren't real, with the most salient being that no one at school ever mentions them – and Touya only ever sees them at the tree in the forest where they first met. That raises the possibility that the child was never at school, but told a lie about being in a different class to throw Touya – and any adults he might tell – off the scent of what's really happening. It doesn't seem like there's any good reason why they'd be kept out of school, and plenty of bad ones, especially when factoring in their subsequent disappearance.

That gets even more interesting when you consider that all of the postcards are instructing Touya to save a child in peril. Perhaps the mysterious friend saw Touya as a savior, or at least as someone they could trust. Or maybe they're testing him to see if he is worthy; his child being ill might, to an unbalanced mind, suggest that Touya's not as good as they believed. But then there are all the fires – the one we know is coming, the one we know has happened at Haru's childhood home, and the one in this volume which may spell doom for one of the characters – it wasn't until this point that I realized that the series' opening didn't say which three members of the family died, and one of the clearly shown items may be more significant than I realized.

Why fire? It feels like an important question. Fire is destructive, and it kills. Fire is cleansing, and it wipes away painful pasts. At this point, I even wonder if someone ought to ask Lemony Snickett if the VFD was active in Japan, there are so many significant ones in this story. If I could figure out the message behind all of the fires, I feel like I'd be a step closer to solving the mystery, and that's either a brilliant use of a red (hot) herring or a carefully seeded clue. It's part of the strength of this second volume and a key factor in making the wait for volume three seem interminable.

The 13th Footprint hasn't yet hit Erased heights of good, but it's steadily getting there. It isn't as clear with its symbolism as Lost Lad London, but it's still a stand-out manga mystery, and Sanbe is very close to the top of his game with this one. If you like mysteries, definitely pick this up – but if you don't like vicious cliffhangers, maybe wait until volume three hits the shelves.