Miriam du Plessis is the mother of Alex du Plessis.
Miriam met Johan when they were both in their twenties but Miriam decided that he was already ruined by his abusive childhood. She decides to save Johan's brother, Roger, as she realises that Johan killed their parents.
Miriam is mentioned by Johan when he appears shocked that Alex's parents would abandon him.
Johan gatecrashes the du Plessis' Thanksgiving which Miriam has cooked.
At first, it seems that Miriam was brainwashed and mean enough to abandon her eldest son.
Miriam was wise enough to realise that Johan was twisted from his childhood. She decided to save Roger even though Johan is her soulfinder.
Miriam is beautiful.
Miriam is adept at hiding things, which is how Johan was unable to track Alex down till he was a teenager.