It turns out that Jamie had travelled back in time to replace an earlier version of himself in the final battle of the first war with the Old Ones. Matt (or the earlier version of him) explains it all to him after the battle (where the Old Ones were initially defeated ... except now, of course, they are back). Matt kept talking about how time was a circle and that's why he and the other four can travel back and forth (I think ... I'm never completely clear on those time travel explanations). In this time period, we meet the fifth of the five -- a girl named Scarlet whose father -- it turns out -- works for the Nightrise Corporation (gasp!).
Anyway, finishing up this book didn't change my mind about Prebble's narration. While I understand the whole point of having the same narrator for an entire series, this just didn't work here. The whole book had an American perspective that Prebble just couldn't manage. When he did use an American accent (seemingly for all the bad guys), he just made them sound like gangsters. And he didn't use an American accent for Jamie or the other young characters that appeared in the novel, which made them essentially indistinguishable from Matt, when he finally showed up.
We put both of the earlier Gatekeeper novels on our list last year, but -- when I went back to review my notes on Evil Star (Book 2) -- I hadn't been impressed. Ultimately, Nightrise was even less memorable.