Krug, one of the Senior Content Designer dropped some very tasty spoilers as to what to expect in the new Chronicles coming next month as part of 2.4

Hey, guys - here’s a heads-up on the Infernal Dawn Chronicle. It takes place in a Sliver universe where Laethys and Maelforge were not defeated and eventually took over Telara. Their former prison has now become their lair to which the Ascended from our world are sent to slay Laethys before she finds a way to enter our universe.

Many of the raid’s mechanics have been kept in place with modifications to allow for duo gameplay. This one will be probably be a little harder than Queen’s Gambit. We still have a couple of weeks of internal testing, balance, and bug fixing, before it goes to PTS early next month
Harder than the Hive Chronicle, stoked already and double stoked that Laethys is the final boss in it.

Laethys is the final boss - as Maeloda surmised, this Chronicle covers her wing of the raid
Krug went on to say Hammerknell will have some new bosses and a new story, looking forward to PTS already

HK is going in a different route, with mainly new bosses and a new story.
Source: http://forums.riftgame.com/general-d...onicles-2.html