This is a book bundle. It has the first three mystery novels in a series. You can also buy each book separetely. 
Book 1 
Four crime-solving friends face off against a killer in San Francisco, Each one holds a piece of the puzzle, #1 New York Times bestselling series of crime thrillers
Book 2
A brutal madman sprays bullets into a crowd of children leaving a San Francisco church, The four crime-solveing friends are back to solve the case Book 2, #1 New York Times bestselling series of crime thrillers, Can't be read as a stand alone
Book 3 
The four crime-solveing friends are back to solve the case, One is hiding a secret so dangerous that it could destroy them all, A fiery explosion rips through the neighborhood, A lost infant and a mysterious message are all that's left, Book 3, #1 New York Times bestselling series of crime thriller, Can't be read as a stand alone