[Astromancer]

Try this one...

The druids were notorious for not writing knowledge down. This meant that once you killed the druids or broke up their educational systems most of their knowledge and tradions were lost. Which is why the PCs are being sent to several different echoes during historical periods when the druids were active and plant listening devices in places where the druids lecture their students.

Given that the druids were noted for being uncannily swift on the uptake and very vengeful, this will be neither easy nor safe.