Which historical mystery would you want to investigate with real evidence?

PastRush: History Detective launches here on 5 November. I'm one of the makers.

Each investigation is a case file with labelled exhibits. You put events in order, compare sources, trace causes and decide what the evidence can and can't prove. Six are free: the Rosetta Stone, Pompeii, the Grand Canyon's rock layers, Ötzi the Iceman, continental drift and the Norse in Vinland.

The new Explorer update adds 245 globe stories, a "Which Came First?" mode (debated dates are left out so every round has one answer) and a map-pin geography game.

A question for history fans: if you could work through one more mystery from the evidence, which would it be? Something archaeological, scientific, or a turning point in history? Teachers and homeschool parents, I'd especially like to hear which topics your students actually enjoy.