What is a summary of The Lost The Dark Ground by Gillian Cross?

Robert was traveling in a plane and then due to the crash he falls in the jungle. He was having no idea that where is he and which place is this. It was about Robert's survival in an incident in his life. He meet some small people of same size of which he was. They lived in the place called Caven over there were small people. Soon he became Friends with them. Robert wanted to find out that what had happened to him and how he became so small. When he could not find it he decided to go back home then he announced to the people of Caven that he was going home and they got angry started his journey with Zak, Cam and Nate. They had some problems in between but they were through them. But unfortunately Nate died. Robert was very sad about it. Then they successfully crossed the road and came to Roberts home. And showed the marigold petals Emma realized that Robert was there. Then the big Robert and the small Robert both touched each others hand and then small Robert become big and told about what happened with him. Then Robert and Emma went to help Cavern members.