DoomwyteLong Patrol Forum member Safronia Cedarwood has posted a summary for Doomwyte that went out to members of the Redwall Readers Club with their Spring/Summer 2008 Newsletter.
Traveller, beware of the Doomwytes!

Set your paws on the track of a great adventure, my friend. Who stole the jewelled eyes of the Great Doomwyte Idol long ago?

What horrors dwell in the caves beneath the wooded hill-the realm of the fearsome Korvus Skurr, black-feathered Raven?

Young Redwallers and their friends find themselves in the grips of adventure, solving mysterious riddles and battling villainous foes in daring underground forays. Join them in the quest, the feasts, the songs, and the fray. Unite with the tribes of the Guosim and Gonfelein against vermin, carrion, and the dangerous Wytes. Discover why the black avenger haunts the wooded slopes. But most of all, beware of the dreaded Balissssssssssss!
From this we can surmise that the treasure spoken of in past summaries seems to be the "Great Doomwyte Idol". We can also glean that the snake seen on the cover is, quite possibly, named "Baliss". As for Gonfelein... that remains to be seen (although it could be connected to Gonff, the most infamous thief in the Redwall Series).

Stay tuned to the Newsline for more details.

(Thanks to Safronia for passing along the summary!)