It is 1920 in an aristocratic household in England. One medical doctor warns the family that daughter Sybil probably is suffering from toxemia during childbirth and the only thing which would save her is to be rushed to the hospital and have a C-section. Another doctor, who is friendly with the Earl, disagrees. In his opinion this is routine childbirth. The baby is born and soon after that Sybil dies, just as the one doctor predicted.
The family, of course, is devastated. The women with authority such as Cora and Mary blame the Earl. Probably the Earl blames himself. But there is no talk about imposing a lawsuit on the medical doctor whose opinion was so wrong. None.
Instead the family handles this tragedy in its own way. Cora won't sleep in the same bed as the Earl. Mary is cold toward her father and writes a note of apology to the doctor whose opinion they ignored.
However, those who believe in lawsuits will be reassured that the old order is crumbling. Matthew, Mary's husband who invested his inheritance in Downton Abbey, is ready to impose modern financial controls. That will usurp the earl's authority. Along the way it could also damage his relationship with his wife.