It picks up right where Tristan ends. Seriously, if you liked Tristan, dive right into Aidan.
Again, I liked Aidan. He actually does seem to have a few flaws. Mostly in the anger management place ...that is exacerbated by his enhancements. They keep calling them super heroes, but I don't really see them as that..but it never got into the twitchy 'dear god, find another term' stage even into book 6. But again, he's a smart ass Alpha Male whining about his papa's murderers.
His enhancement is definitely more believable than Tristan's. And everything's chugging along fine...until they start talking about time machines and the Nazis coming forward in time. I sucked it up and kept reading, but if you want someone to take your Nazi German Time Hopping Squad of Doom seriously, it's probably best not to name the chief bad guy VonFussenhoffer. Again, VonFussenhoffer. Luckily, she doesn't ask you to take anything seriously in this series, so I suppose I can forgive it...even if my coworkers will never forgive me for giving them the basic rundown of the book. They're not as open minded about the silliness as I am.
Oh look, Rachel shows up again, can we punch her now? No? Will Cassandra? Damn it. I liked Cassandra...although I would have loved to have seen her kick more ass before it was all said and done. It's kind of like the author forgot all the sassiness and fight that she'd had in the beginning, and left it in the time machine so that Aidan wouldn't have any competition for toughest bad ass in the book. She was allowed to keep the sassiness for banter purposes, but no more kicking ass, because then Aidan wouldn't need to rescue her or something. I dunno.
Oh look, there's book 3! D'Artagnan! I like that character, seems to have what could be actual to honest goodness depth, and the best line of the series as she winds together the family trees of all the characters...and seriously... We don't have the time or the sanity to delve into that in these reviews.