DI Sue Manson has to find a missing heiress whose abductor appears to have an obsession with twins.
The riddle left by Amy's kidnapper leads Sue and her police colleagues to the first of many bizarre locations.
Angela agrees to be hypnotised by Fred, in the hope that her psychic connection with Amy will yield some information.
The kidnapper's latest taunt leads police to the National Gallery.
At home, Sue cannot avoid a row with her mother.
The hunt closes in on the kidnapper as the police find the key that connects the locations across London.