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Fire burns up and out.

Like a V

It ignites at the base of the V and flames up – because fire burns up, where the oxygen is – and out, as the atmosphere in the room tries to equalize the heat and pressure.

It burns up and out from its point of origin and often it leaves a V-pattern mark. In which case the fire points to where it started.

Now, when a fire starts in the middle of the room, you're not going to see a V-pattern, because there's no surface for the fire to mark. When a fire starts away from a wall, what you'd expect to see instead of a V-pattern is a circular pattern on the ceiling above the point of origin.

Which there certainly is. Above the bed there's not only a circular burn pattern, there's a freaking hole blown through the roof. But there's also ankle-deep ash and deeper char on several places on the rafters and there's a hole in the roof and there's a dog barking outside.

Jack starts in what used to be the closet.

The closet is a walk-in.

Or a hike-in, because this closet is maybe a little smaller than Delaware.

And calf-deep in ash, which Jack would expect because there's a lot of stuff in closets. That's the purpose of a closet, right? To put stuff in it, and because this is a humongous walk-in closet belonging to rich people you're going to expect that the alligator had a banquet in here.

Especially if you have clothes hanging from a pole, because fabrics are tasty to eat and you also have a lot of nice oxygen underneath them. And you're going to have a lot of ash because you're going to have a lot of "fall down." Fall down is just what it sounds like; it's stuff that burns and then falls down onto the floor.

Again, the basic principle of fire is that it burns up. It burns up, seeking oxygen and fuel. Insufficient oxygen, the fire smothers. Insufficient fuel, the fire burns out. The situation a fire really likes is when it can burn upward and find fuel there. Fuel like clothing. Fuel like boxes stored on shelves, and then the shelves themselves.

So the fire zooms up and consumes those things, and the carbonized material – char – falls down on the floor. A lot of times there's enough fall down to smother the fire on the floor. That's why you can go into a fire site and the ceiling is burned but the floor – where the fire started – isn't.

See, sometimes fire will go up and then across. The fire isn't even burning across the floor, it's up along the ceiling, where the fuel is. It burns the nice fuel up there and gets hotter and hungrier and then you have what's known as the convection effect. The fire up top generates so much heat that the heat – not the flame – ignites the material on the floor and then the floor goes up.

But it all has to start somewhere.

Which is at the base of a V, and the reason Jack's looking in the closet is because Jack is a cynical bastard.

A cynical bastard thinks that if someone is going to start a fire, the closet is a good place to do it because it's not immediately visible and the fall-down effect often obscures the evidence.

So Jack's down on his knees digging away the ash at the back wall of the closet and it doesn't take long before he finds what he's looking for – a tall narrow V marking on the wall. Important that it's narrow instead of wide. A wide V is the fire telling you that it spread normally, just the usual grazing on the usual feed. A narrow V is the fire telling you something else.

The fire saying, I was hot.

I was fast.

Something else with this V. The apex doesn't come to a point. It looks like a V with the point cut off, more like V.

Which is the fire hinting to Jack, Yo, dude, maybe I had a little help. A little boost. Maybe I had me a little something to get me, you know, started.

In an accidental fire, the V will be pointed. But if the fire had a little help – say, if someone poured an accelerant on the floor – then the apex of the V is going to be as wide as the pool of the accelerant. Because you don't so much have a point of origin as you have a pool of origin, all of which ignites at the same moment.

So now, Jack thinks, we have not just one point of origin, we have at least two.

Which is one too many.

If there's one thing Jack knows about an accidental fire, it's that it has one – count them, one – point of origin.

An accidental fire doesn't start accidentally in two places.

It's not possible.

Jack pushes aside the charred remains of what appears to have been some coats on the floor by the wall at the bottom of the V.

Could swear he hears the fire laughing.

Because there's a hole in the flooring. As wide as the base of the

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