The beautiful eighteen year old Karla Stanton, who is living in the country with her brother training horses, is astonished when her half-sister Penelope, now Lady Melford, who is renowned as a great beauty in London, unexpectedly calls on her. She wishes Karla to disguise herself as her aged aunt and chaperone and to go with her to Paris where she intends to spend three days, ostensibly shopping for clothes, but actually to be with the Marquis of Welbourne, who she is having a passionate affaire-de-coeur with.