Iron Curtain is Book 3 in the "Metal Heart" trilogy.
Eleni Garza and Rabbit Santiago reunite after their cross-country adventures to attempt to develop and distribute a cure for the nanovirus. However, in order to save Rabbit's life, Eleni must sacrifice their easy shot at the cure and merge him with the Alpha System, the artificial intelligence she secreted away from the KERN lab.
Together, she and Alpha rescue Scarlett Buford from the Mexico City war zone and travel to New Orleans, Louisiana to save her brother Logan. But when those efforts are all thwarted, their final destination will take them beyond earth, to the last refuge for the cure: the Iron Curtain.