Proto: How One Ancient Language Went Global, by Laura Spinney. Other than those brianworms it's a really good book. I had been reading David Anthony's The Horse, The Wheel, and Language but got bogged down in pottery types. Started Proto and immediately learned just how much has changed in the field even since Anthony's book was published in 2007.

Although there's talk of the historical linguistics aspects and how linguists know how to chart the changes that took place, it also makes use of genetics and anthropology to examine how a language of steppe herders managed to dominate Eurasia without (necessarily) involving massive campaigns of conquest. (No need to be wary of the genetics aspect - it's to figure out chronology and not to imply anything untoward or nationalistic.)

Edit - As for Linear B - The Decipherment of Linear B by John Chadwick is excellent. Chadwick must have been a great teacher; it's as definitive as any "definitive introduction" I've ever read.