Kainnan: The Switch by Belinda Stott

Back on Earth after nearly losing their lives on the alternate world of Kainnan, Noah, Katerina, Summer and Ryder are desperate to catch and eliminate the tyrant Wilhelm once and for all.  Yet within hours, one is kidnapped, one poisoned and one set up for assassination, whilst Wilhelm is in control of a new and deadly weapon. With both Kainnan and Earth in jeopardy, dangerous plans are set in motion to save the three and stop Wilhelm. But it is Summer who will face the greatest challenge - confronting the pain in her past in an attempt to win freedom for them all. 
 
Fast-paced yet deeply moving, The Switch weaves together dangerous exploits and nail-biting suspense with introspective, honest and tender moments.