Feldane recently sealed a marriage alliance with Chantris; Feldane pursued this avidly. The arrangement was that Stuart Feldane, the Feldane heir, would marry the oldest Chantris girl, Penelope. This was a state marriage; there was no illusions that the couple were in love.
Stuart, a very dutiful heir, made uncharacteristic protesting noises at the marriage. His parents dismissed this idea (and Irene went to Fiamme of the Order of Clarity for a judgement; when Fiamme suggested an apology, Irene offended her by ignoring the Order's judgement). So, ironically, it should have been no surprise when Penelope became accused of infidelity and breach of contract.
Stuart heard accusations against her and challenged his rival to a duel. The rival asked Penelope to reason with Stuart. She was delayed, and showed up at the duel as it was underway, calling Stuart's name. Distracted, he looked up - and was killed by his opponent.
The sword that killed him was a Feldane sword (Stuart chose the weapons); it trapped his soul in it. But the damage was done. Feldane and Chantris erupted at each other and Penelope is sent to the country to die down the scandal; she was killed on the way by brigands. Feldane, incredibly, insisted that the marriage contract stand and Errol, who was Stuart's second at the duel, became heir and engaged to Dulcinea Chantris.
Stuart was an ideal heir, and his loss was telling. Irene keeps him in the sword on the wall and complains to him. Errol has been promoted to heir, but he is also unaccustomed to the role, and has been out raising hell and ignoring his fiancee, Dulcinea Chantris. Addison has been recalled from his happy go lucky life as an at-best-casual barrister in shadow to learn up on being the heir's understudy. He does seem to want to argue on behalf of the rights of the common man, an attitude that Irene finds distressing. Taleyn is just back from completing her education; as the daughter, she is being primed for a profitable marriage.