Commander Una faces court-martial along with possible imprisonment and dishonorable dismissal from Starfleet, and her defense is in the hands of a lawyer who’s also a childhood friend with whom she had a terrible falling out.

An accident with an experimental quantum probability field causes everyone on the U.S.S. Enterprise to break uncontrollably into song, but the real danger is that the field is expanding and beginning to impact other ships—allies and enemies alike.