The Surprise of Haruhi Suzumiya (light novel)

"The two storylines from The Disassociation of Haruhi Suzumiya continue, introducing a new inductee into the S.O.S. brigade who may be more than just the eager freshman she appears to be. As the two realities converge, the SOS Brigade learns that the new member may have the ability to bring the two story 'timelines' together--and save the world in the process"--