It is 3000 years after the events that take place in Ender's Game and Ender Wiggin is alive and well, as is his sister Valentine. Having spent the majority of their adulthood travelling through space, relativity allows them both to be only in their 30s age-wise and yet they have both witnessed the progression of mankind for over 3000 years due to Ansible communications technology which allows for instantaneous communication across the vast distances of space. The Starways Congress has been created in the wake of the xenocide of the buggers and a new form of religion has been formed based on the writings of Ender Wiggin. Speakers for the Dead are now called upon to speak the truth for the recently deceased. Speakers are expected to neither condemn nor forgive the actions of the deceased, but rather shine the light of truth upon them so others can draw their own conclusions. Speakers are given ultimate access to the records of deceased individuals and anyone may request a Speaking. Once a Speaker is called upon and accepts the task the Speaking can't be stopped and the Speakers themselves have rights and powers protected by the laws of the Starways Congress to fulfill their duty. Since space travel still takes significant time it is not uncommon for a Speaker to arrive at a Speaking destination many years after receiving the initial request via an instantaneous Ansible transmission.
Ender himself is now a Speaker when he receives a call to speak for someone on the colony of Lusitania, which is also the location of a newly discovered alien species. Ender accepts the Speaking and brings with him the dormant Formic Queen when he departs for Lusitania, leaving behind Valentine for the first time in his adult life. This is a story full of religious and political intrigue, and it focuses on mankind's struggle with the challenge of properly interfacing with an alien species that is far less technologically advanced.
Like its predecessor, this book won the Hugo and Nebula award when it was published, but I found it to be a little slow and plodding when compared to the events of Ender's Game and this one will not be for everyone. Orson Scott Card considers Ender's Game to be merely prologue and background for this book, which is the story he really wanted to tell, but I'm not sure it is the better tale. It is certainly deeper and more thought provoking than its predecessor, but ultimately for me it was less entertaining and less engaging. In audiobook form Stefan Rudnicki returns as narrator from the first book and is joined by David Birney to deliver a solid reading.
Perhaps you should give this one a try and draw your own conclusion.