The single-player campaign's description is as follows:
"Mass Effect 3: Leviathan is the first story-driven, single player DLC to be made available since Mass Effect 3 Extended Cut. Leviathan expands upon the events of Mass Effect 3 with gripping and emotional storytelling, compelling new characters, powerful weapons and unique upgrades. Players will be able to discover more about the origins of the reapers as they race across the galaxy to unravel the mystery that surrounds the fabled Leviathan."
Update: Leviathan will launch this summer for PS3, PC and Xbox 360, EA announced at its Summer Showcase today.