"The Legend of Korra" Book 2 has just aired its third episode, but it seems new voice actors are already being cast for Book 4.

An interesting tweet from actor Jason Marsden appears to be hinting at working with Jason Isaacs, Anne Heche, and Kiernan Shipka on a new project.

Just worked with Jason Isaacs, Anne Heche, and the little gal from Mad Men. Great start to the day! #korra

— Jason Marsden (@JasonMarsden) September 19, 2013

Given the hashtag, it seems fair to guess that Marsden is referring to "The Legend of Korra." And knowing the team is currently doing production work for Book 4, perhaps we will see some of these familiar voices in the future.

The "little gal from 'Mad Men'" should be referencing Kiernan Shipka, who plays Don Draper's daughter Sally. Jason Marsden is a voice actor with a long list of voice work including "Tarzan" and "Ben 10: Ultimate Alien."

Jason Isaacs, meanwhile, is perhaps best known for playing Lucius Malfoy in the "Harry Potter" films. Anne Heche has had a long career in film and TV, most recently seen in the HBO series "Hung."

Hopefully with production so far ahead, the hiatus between each Book will be shorter for "The Legend of Korra."

In the meantime, fans should enjoy Book 2 of "The Legend of Korra," even if they can't catch the show on Nickelodeon every Friday night.

Currently, Nickelodeon is uploading each episode following the live premiere, and the latest episode "Civil Wars Part 1" can be seen on the Nickelodeon website.

Check it out below: