The Mystery Club is back-and the stage is set for their most dangerous case yet. Emma, Maya, and Jayden thought their last adventure was behind them. The play is over, the creepy notes have stopped, and the custodian Mr. Thompson isn't chasing them through hallways anymore. But when the school auditorium starts to hum again, they realize the danger never went away. Something powerful is hiding under the stage-a machine that feeds on sound, and it's waking up just in time for the biggest performance of the year. With the help of the one adult they least expected to trust, the Mystery Club must face secrets bigger than Ridgewood Middle itself. The lights are hot, the crowd is loud, and one wrong move could turn opening night into the final curtain. Will the Mystery Club silence the machine before it destroys more than just the play? Or will their voices become the fuel it's been waiting for? The Echo Under the Stage is the thrilling second book in the Mystery Club series-a fast-paced middle-grade adventure about friendship, courage, and finding strength in the unlikeliest of places.