Intrepid canine detective Chet accompanies his human police officer partner, Bernie, on a first assignment involving the disappearance of a teenage girl who ran with the wrong crowd, a case that is complicated by Bernie's dysfunctional personal life.

On a spring morning in 1951, eleven-year-old chemist and aspiring detective Flavia de Luce gathers with her family at the railway station, awaiting the return of her long-lost mother. Flavia is approached by a tall stranger who whispers a cryptic message into her ear. Moments later he is pushed under the train by someone in the crowd. Following a trail of clues, she unravels the deepest secrets of the de Luce clan, involving none other than Winston...