I wasn't sure what to expect from this book, but what I got was a history of the English language based on 100 words. Crystal explores the origins of each of his 100 words in chronological order based on when they first appear (a few entries are more conceptual e.g. #60 Species is about the species naming system devised in the 18th century rather than the origins of the word itself). So for example, you have #3 and (8th century), #11 bone-house* (10th century) through #63 Hello (19th century). [Aside: hi (15th century) is older than hello and hey (13th century) is even older.] It keeps going through the 20th and 21st centuries with words like #89 PC, #97 Muggle, and finally #100 Twittersphere.
I've also apparently picked up some "eastern" emoticons according to #94 LOL without even realising it. o.O
*bone-house: a living human body