***SPOILER ALERT!*** 
 In the future Earth has been taken over by a unique alien species. The infiltration was slow and undetected until it was too late. Now these aliens, known as Souls, live inside human bodies, which act as hosts for the invading parasites. Usually when a Soul is placed in a new host it is able to take full control of the body, pushing aside any remnant of the human consciousness that once lived inside. 
 After a Soul named Wanderer is inserted into her new host she soon realizes something isn't right. It seems the human who once inhabited this body refuses to give in and die. Melanie Stryder wants no part of Wanderer and is doing everything she can to fight back. Even though Wanderer controls the body, nothing she does is able to quench Melanie's spirit. She is always there, in her head, so to speak. 
 As time goes by Melanie's memories become Wanderer's and soon she finds herself longing for the people that meant so much to her host. Melanie left behind her brother and the man she loves, and now Wanderer has developed those same feelings. Soon Wanderer and Melanie begin working together to track down Melanie's loved ones, all the while being careful that they don't lead the other Souls to the humans who are in hiding. When they finally do find them, they must figure out a way to live peacefully with a group of humans who have grown to hate Souls. Emotions flare and relationships are tested in agonizing ways as two lives must share one body and as enemies must learn to co-exist and survive. 
 The whole thing had me crying. The ending was pretty much terribly weepable. lol It's sweet, and strong. I loved it.