As the title says Episode 4 is airing today April 28th at 10am Central or 11am Eastern time which is 3PM GMT.

K104 Screenshot

Also check out the episode preview before watching :)

http://www.youtube.com/watch?v=znS4RpEhM-k

And here is the episode description

“Korra is recruited to join Councilman Tarrlok’s task force which tries to rid the city of Equalists.”