Burning a pair of shoes

My protagonist has been kidnapped! After being prepared for sacrifice and put through some very scary stuff, he escapes by the skin of his teeth only to find his captor has burned everything he was wearing when he was taken. In the ashes of the fire, he finds some recognisable remains such as buttons, together with the remnants of his shoes.

Here's my problem. What would the fire do to the shoes?

He was quite smartly dressed (for some value of "smart" that is mostly, shoes aside, assembled from the Oxfam shop) so I expect they'd be leather, but the soles would be plastic.

Any helpful details, such as the smell, would be gratefully received. Also, how likely are they to still be wearable in an emergency? So far I have assumed that they aren't, so he has to walk barefoot to the nearest shoe shop and buy new shoes with money stolen from his captor. I'd like to keep things that way if possible, but I don't think the character would agree with me. He's used to making do with very little, and he'd like to wear the shoes if they would stay on his feet. So I'm hoping they wouldn't.

I don't know what she used. Something that would work. She doesn't mess around.

I assume she lit the fire outdoors, because of the smell. Thinking about it, she probably shoved the clothes in some kind of drum-shaped container to keep things neat (I've just had a great idea for what kind) and poured petrol on them. She didn't have a lot of time to prepare, and she probably didn't have a handy supply of wood.

An oozy mess of melted tar-like stuff sounds like what I want. Just as long as my MC can figure out what got burnt, so he doesn't waste time (and words) hunting for his clothes elsewhere. That's why he was wearing a jacket with distinctive metal buttons.

Thanks to everyone who replied. I think I can get it right after your help.