Found by Margaret Peterson Haddix

Jonah and his neighbor Chip are 13 years old when they start getting mysterious letters in the mail. The first letter says, “You are one of the missing.” It turns out that both boys were adopted as infants and they begin to wonder if that is why they are getting the letters. With a little investigation they find the name of an FBI agent who may know something, and in a hostile meeting with him they acquire a list of names of “witnesses” and “survivors.” They have no idea what they are dealing with, but they begin making phone calls. Things quickly get serious and mysterious and they suspect they are involved in something sinister that may involve time travel. I don’t want to go into anymore detail here and ruin any surprises, but I will say that this book is obviously a set up for a series that will take a group of 36 kids on an array of adventures throughout history. Haddix has an interesting idea here, but I’m afraid it may be too far-fetched to work. It certainly leaves the reader hanging at the end and waiting for a sequel, which some readers will like and some will not.