The Past Is Gone by James Valentine
Just when Jules finally gets up his nerve to ask Gen on a date, Theo pops in to their life. He literally pops into Gen's room out of nowhere. He's a time-jumper from the future and is mistakenly sent to Mil 3, which is our present day. Apparently in the future, time-travel is common place, but the jumpers are invisible to the people of the current time. Only, something has malfunctioned in Theo's jump and he's visible. Jules and Gen work with Theo to try and return him to his own time.
Okay, not a bad start to a trilogy. I really found the description of the jumps and life in the future fascinating. The story is fairly predictable, but it's still fun to read. Of course, you have the evil person from the future who wants to keep something about the time jumper machine a secret. No one knows much about this yet, so we're left with a cliff-hanger and a tease of the next novel. Of course, I want to get the next one to find out what happens. C+ rating.