The Tsar's Bride
The story is supposed to take place in the autumn of 1572 in Moscow.  At this time Russia was ruled by a very cruel tsar called Ivan the Terrible.  Tsar Ivan had a group of people who guarded him.  They were called oprichniki.  The oprichniki were like bodyguards, but they were told to kill anybody who was not loyal to the tsar,  so they behaved like terrorists, killing, raping and stealing wherever they went.  In the opera there are also “Boyars”.  A Boyar was a nobleman.