Hollow City by Ransom Riggs. Spoiler Alert

The Hollow City by Ransom Riggs is a sequel to Miss Peregrines Home for Peculiar Children. It follows a group of peculiar children; meaning they have special powers, and are believed to have two souls, one in which normal people lack. However, these powers come with great responsibility and danger. Their headmistress was turned into a bird, which is called a ymbrine. The group of children have to get to London, during World War II, with monsters called hollowgasts and wights trying to hunt them down. They have to be able to trust one another because without trust, they have nothing but

Jacob, the main character, is able to sense and see hollowgasts, while they are invisible to humans and other peculiars. He is the new one in the group. The others had to learn to trust him and his abilities. They also have to put their trust in one another. They need to be able to know that someone is there to protect or help fight off any wights or hollows. They also have to know who to trust and who not to trust. Usually, they trust no one. But there was a special group of gypsies, who helped the peculiars in extreme ways. Without trust, they might have not been able to make it to London to help their ymbrine, Miss Peregrine.

The trust that the peculiars share keeps them alive in many ways. Their powers can only take them so far. However, if they are unable to trust each other, they aren't able to protect each other, and themselves.