Rejuvenation Book 3. Rejuvenation Trilogy, #3

Out of a clear, blue sky, a mysterious alien race wreaked havoc on planet Earth, thus beginning the Melter War. Alien energy weapons struck the Polar ice caps. Oceans rose, drowned huge swathes of land, swallowed up great cities and left much of the earth as an irradiated wasteland. Millions of people died. But a saviour emerged; Lisette Fox and her Belus Corporation supplied the weapons and technology to defeat the Melters and brought peace back to the world.
Some two decades later, Bobbie Chan, a child at the outbreak of war, now works as a doctor caring for the ultra-elderly. Bobbie encounters a previously unidentified disease, 'Rejuvenation', which makes the old young but has homicidal side effects. In this gripping final instalment of Byddi Lee's Rejuvenation trilogy, Bobbie discovers the shocking truth behind the Melter's attack and Rejuvenation. Bobbie faces a decision with untold consequences, not only for Bobbie but for the entire human race.