Apparently, I totally missed out on this but... there is a cover for the final Gallagher Girls book (and a title) UNITED WE SPY.
I actually saw the UK cover first, and then went to look the US one.
Anyway, summary, such as it is now:
Cammie Morgan has lost her father and her memory, but in the heart-pounding conclusion to the best-selling Gallagher Girls series, she finds her greatest mission yet. Cammie and her friends finally know why the terrorist organization called the Circle of Cavan has been hunting her. Now the spy girls and Zach must track down the Circle’s elite members to stop them before they implement a master plan that will change Cammie—and her country—forever