S1·E20 Episode 20 (a.k.a. The Finale)

Catherine and Andrew are at the shop with Old Nicholas, who informs them of what will happen once Nicholas has choosen the correct agent. At the ball, Frid decides to get Sir Ivor back, only to make an idiot of himself by producing the drum of cooking oil. Sir Salisbury, Sir Ivor and Frid are all arrested. When Jade goes through the mirror and tells Nicholas to chose the other one, he decides on the agent and mixes into the drum. Back in 1995, Jo and Tama collect the ring and go back to Jo's house where Louisa and Nicholas are waiting. Nicholas finds however that he can't go back to 1919 with the ring. He makes the decision to stay and the mirror vanishes just after Louisa returns home.