Party get past one mimic (befriended and now caleld Yarwood) who indicates the location of the treasury guarded by another evil mimic. Party enter and take it on - killing it, get lots of treasure
In (now) empty treasure room they find a scorched piece of paper, implicating someone 'top-side' was in league with Casmagin the child stealer. signed with a seal of a Kingfisher with a scroll in it's beak. - a sign of a local messenger service.