Caught in the Light (Unabridged‪)‬

On assignment in Vienna, photographer Ian Jarrett falls suddenly and desperately in love with a woman he meets by pure chance, Marian Esguard. Back in England, he separates from his wife and goes to meet Marian at an agreed rendezvous, only to hear her tell him on the telephone that she will not, after all, be coming. Then she vanishes from his life as mysteriously as she entered it.

Who and where is the woman he met and fell in love with in Vienna?