This might be the least engaging mystery I've ever watched.

Some random guy we don't know called Eugene was hit by a car and died. Not sure why Torchwood need to investigate a random hit and run, but who cares? They decide that the cause of death was by hit and run. This should be case closed. I appreciate we the audience know that Eugene is hanging around as a ghost (or whatever he is). But, the Torchwood team don't, so there's no reason to keep investigating.

But Gwen does, because something apparently doesn't add up. Like... umm... the last thing he did on his phone was to take some photos of some random shoes (hey that's the title of the episode). What could these shoes mean? Well nothing, he just accidentally took some photos whilst holding his phone.

I think the justification is that Eugene was a Torchwood super fan, who followed the team around and kept trying to get Gwen to look at his own "alien" artifacts and investigations, only to be politely dismissed each time. Which causes Gwen to feel guilty for not talking to him more or something, and then she'd be compelled to get to the bottom of his death (and apparently fall in love with him or something whilst doing so). Except the secret about his death was that he got hit by a car, a thing we all knew from the very first scene. There's no mystery here. He got in an argument with his friends about some MacGuffin that is apparently an alien eye, then ran off upset and didn't watch where he was going whilst crossing the road.

The only thing mysterious about the death itself, is that Eugene's ghost is hanging around afterwards. A thing the Torchwood team don't know until the end of the episode, so it doesn't justify anything Gwen does before then. The reason this happens is because Eugene swallowed the alien eye to stop his friends from stealing it (it's worth a good amount of money). I don't think the episode even gives much explanation as to what the eye is or why it can keep a persons spirit around after death either though. So the mystery isn't even well explained.

The episode is trying to give the nice "enjoy life, live each day" message. It does this in a very heavy-handed and corny way. But it's a nice enough sentiment. Honestly the episode, much like the character Eugene is relatively sweet and well-meaning. It's just also feels like a complete waste time.