The truth comes out when Hamish and Simon's daughter plan to marry, and must be stopped. The belatedly acknowledged past takes its toll on us. So it does with us all. Histories hidden or denied avenge themselves. We collude in our ignorance of pasts that will shame or wound us.
Partial amnesia is necessary to ongoing life.
We all crave a past we can love. Yet selective oblivion, whether imposed or self-induced, can cripple present action and future purpose. Those past-obsessed, like Simon Challenor, notably warp what they let themselves and others know. Disaster often ensues. It is baleful to be haunted by heritage, a realm beyond rational discourse.