The fourth in the Ender’s Game series.  Well… there’s a reason why a “trilogy” is a thing and a 4-book series is not.  Perhaps by book 4 an author just needs a rest or a change in scenery – maybe a trip to Risa?  There’s altogether too much bitching between the main characters in this novel.  Also somewhere in one of the last books instantaneous space travel was invented which I don’t approve of.  It makes it too easy to pop in and out of any situation.  There was a reason why the universe was given the speed of light and causality, and it was to add discipline to novels.  The viruses are pretty good though.