A year ago, six friends attended a seance when the Clairvoyant made two revelations.

First, that one of the party was harbouring a terrible secret.

Second, that the secret would kill them.

Now a year has passed and Olivia Valance has been found dead, lying in the hallway of her own house, the doors locked, no sign of external injury. Mysterious? Yes, but she is little mourned by colleagues or neighbours.
An interfering woman who nobody seems to have liked, Olivia was also the Agony Aunt on the local paper, so did that give her one private secret too many?

If so, whose?