Future Threat by Elizabeth Briggs

Six months after returning from their first time-travel mission, Elena and her companions are drafted into a rescue effort to find a missing team of time-travelers.

Six months ago Aether Corporation sent Elena, Adam, and three other recruits on a trip to the future where they brought back secret information--but not everyone made it back to the present alive. Now Elena's dealing with her survivor's guilt and trying to make her relationship with Adam work. All she knows for sure is that she's done with time travel and Aether Corporation. But Aether's not done with her--or Adam, or fellow survivor Chris. The travelers on Aether's latest mission to the future have gone missing, and Elena and her friends are drafted into the rescue effort. They arrive in a future that's amazingly advanced, thanks to Aether Corporation's reverse-engineered technology. The mission has deadly consequences, though, and they return to the future to try to alter the course of events. But the future is different yet again. Now every trip through time reveals new complications, and more lives lost--or never born. Elena and Adam must risk everything--including their relationship--to save their friends.