Shall we date?: Rewind

Who was it that died then?

"Time Reversal"
I've been able to solve many mysteries with this power.
(Oh yeah, and my childhood friend Walt has helped along the way!)
And now, we find ourselves here at Shielah's house.
Eight of us, all about the same age, have gathered here to prepare for a festival.
I was really hoping we could all get along, but things have turned sour pretty quickly!
It looks like we've got a case on our hands to solve.

There's no way I'm letting the culprit get away.
Don't you dare go anywhere, scoundrel!
I'll do what it takes to stop you!