Anakin, Obi-Wan, and Mace Windu as they were in RotS take on three lords of the Dark Side: Darth Caedus, Lumiya, and Darth Malgus. Setting is The Invisible Hand Observation Tower where Anakin and Obi-Wan fought Dooku.
Note that by Mace Windu as he was in RotS I mean Mace Windu with his amp. Anakin is also still Light Side. Also, Darth Malgus is the way he was in the actual The Old Republic MMORPG.