The perfect crime

Stephen Berry is about to jump off a bridge, but is stopped at the last moment by a counsellor from a suicide prevention centre. But a week later, Stephen is found dead at the bottom of the abyss beneath Tantallon Castle. Did he jump off the walls himself, or did someone push him? More detailed enquiries reveal that there have been other suspicious suicides in Edinburgh. How does a serial killer choose his victims and who's next?