In the summer of 1974, a heat wave blankets Boston, and Mary Pat Fennessy is trying to stay one step ahead of the bill collectors. Mary Pat has lived her entire life in the housing projects of Southie, the Irish American enclave that stubbornly adheres to old tradition and stands proudly apart.One night, Mary Pat’s teenage daughter, Jules stays out late and doesn’t come home. That same evening, a young Black man is found dead, struck by a subway train under mysterious circumstances.The two events seem unconnected. But Mary Pat, propelled by a desperate search for her missing daughter, begins turning over stones best left untouched — asking questions that bother Marty Butler, chieftain of the Irish mob, and the men who work for him, men who don’t take kindly to any threat to their business.Set against the hot, tumultuous months when the city’s desegregation of its public schools exploded in violence, Small Mercies is a superb thriller, a brutal depiction of criminality and power, and an unflinching portrait of the dark heart of American racism. It is a mesmerizing and wrenching work that only Dennis Lehane could write.