The girls, many of whose names start with the letter J, find themselves quarantined for measles, which was and is a life-threatening disease in many parts of the world. The virulent anti-vaccine lobby should read this book to teach them what the world was like before herd immunity existed, i.e. COVID-19. But the first half of the 20th century was a time when young and old died of measles, polio, mumps and rubella. However, the quarantine doesn't stop Jen and Jackie from having all kinds of adventures!