There is sex, there is scandal, there is betrayal—in other words, everything you’d expect in a good courtroom drama.  Emma Donoghue based The Sealed Letter (Harcourt, $26) on a real divorce case in 1860s Victorian London.  The players in this drama: Emily “Fido” Faithful, early feminist, accomplished businesswoman; Helen Codrington, beautiful, bored, impetuous; Harry Codrington, distinguished Admiral, husband of Helen.  When Helen embarks on a dangerous affair with a young officer, she recruits her friend “Fido” to help cover her tracks.  But when Harry discovers the affair, the lid is blown off their unhappy marriage.  Fido must choose between the friend she loves and the truth.  But what is the truth?  Who has betrayed whom?  Great writing by Donoghue propels this story to its dramatic and surprising conclusion.