What is the name of fifth book in Children Lamp Series?

There is no fifth book in the "Children of the Lamp" series. The series, written by P.B. Kerr, consists of four books:

1. Children of the Lamp (2004)

2. The City of Ember (2003)

3. The People of Sparks (2005)

4. The Prophet of Yonwood (2008)