I actually still have two first generation Cynster books left to read (the final two sisters), but this one
In many ways the plot of By Winter's Light is slight. The action takes place across only a couple of days, there is a great deal of feasting and merry-making, and most of the actual drama is unrelated to the romance, which is basically about Claire sorting out her own thoughts in her head. As I finished it, I thought to myself, 'If Laurens wrote Chalet School fiction, this would be it.' There's a group of young people trapped in a cottage by a snowstorm, and on another occasion, a number of children play on an icy stream, with not-unexpected dramatic results.
It's a Christmas story, and a gathering of the clans, and the romance isn't even among the Cynsters themselves, but between the tutor of Alastair and Phyllida's sons, and the governess of Gabriel and Alathea's daughter. The setting at Casphairn Manor (seat of Catriona) allows for a totally snowed in Christmas tale, and sets the scene beautifully for the next two novels (focused on the eldest twins of Catriona and Richard - Lucilla and Marcus).
The romance is satisfying, and even when the main characters are not aristocrats but "members of the household", Laurens' heroines still get to have sex before getting married. (Although in this case that's less of a shock to the standards of the day, as Claire is a widow.)
I don't think missing this book would do anyone any harm in terms of understanding the rest of the series, but it was a lovely, light read, well suited to reading over a couple of days while still sick in bed.