When Susannah Makepeace's mother dies, she and her older brother, Dominic, are left orphaned and homeless in late 17th century England. Dominic decides to travel to the New World of America in hopes of making his fortune, and so Susannah must go to live with her wealthy, distant cousins, the de Gracys, who have a large estate, Gracy Park. Susannah hates having to live off of the charity of relatives she has never before met, and knows it may be a long time before she is reunited with Dominic.
The de Gracys provide Susannah with a comfortable cottage to live in, but she misses her brother and feels terribly lonely. Her cousin Juliana, who is close in age to Susannah, is haughty and unkind, and Susannah's only friends are Bid, the maid provided for her by the de Gracys, and Ned, a young man who was a friend of her brother and who used to work for the Makepeace family. When Susannah learns that her brother has arrived in America but is very ill, she decides she must somehow obtain enough money to travel there and help him, even if the only way is becoming a highwayman and stealing the money.
Highway Girl is written as Susannah's diary, making it a quick and easy read. Overall it was an enjoyable book, though it does have a few flaws. Despite the title, Susannah becoming a highwayman doesn't occur until late in the book, and so it doesn't play a significant role in the plot of the book, which is mostly about her everyday life in Gracy Park. It was also a little unbelievable how quickly Susannah turned to robbery to help her brother, since it seemed a bit out of character for her, and the ending was a bit abrupt and too perfect. However the book was overall a pleasant read. Although this book is not one of my top favorites from the My Story series, fans of the series should enjoy it.