Ann Talbot
Ann Talbot was an aristocratic young woman physically almost identical to the Doctor's companion Nyssa. Unlike Nyssa, she had a mole on her left shoulder.
Profile
The Doctor and his friends met her in 1925, at a cricket match and fancy dress party at Cranleigh Hall, in rural England. Formerly engaged to George Cranleigh, she became the fiancee of his brother, Lord Charles Cranleigh, after George was presumed dead during his hunt for the rare black orchid. (George had not, in fact, died--but tortured, mutilated and driven violently insane by the Kojabe tribe.)
At a fancy dress ball, Ann and Nyssa wore the same butterfly costume, in order to prank the other guests. (DW: Black Orchid)
Ann married Charles Cranleigh the following year. The Doctor attended the reception and asked a favour of the new Lady Cranleigh: that she impersonate Nyssa as part of an elaborate plan to defeat the Osirians. (MA:The Sands of Time)
Other appearances
Ace, searching for segments of the Key to Time, briefly re-visits the events of Black Orchid in Time & Time Again. She sees a woman who is either Nyssa or Ann Talbot (she cannot tell which) but does not approach or speak to her.
