johnnyreb,
The Beekeeper's books involve mid-60's Holmes falling in love with and eventually marrying a very young Mary Russell. In the first book, she's a precocious adolescent of 14, and it's one of the best books I've read. Great twist as to the final villain.
In the second book she's coming into her own as an adult, developing this on again/off again attraction to Holmes, and it reads a lot like a bad romance novel. Really, it's very skippable, though it does involve a pretty good mystery.
The rest of the series, maybe 12 or more, she's a full adult, married to Holmes, but quite independent.
The first, while light and fluffy, is one of my favorite books of all time. The rest are worth reading if you can make it through the second, but no great loss if you don't read them at all.
Also, you might want to never read "Shadows Over Baker Street," a Holmes/Cthulhu Mythos mashup!