The Summer Children (The Collector, 3, Band 3)

This FBI agent has come to expect almost anything―just not this…
When Agent Mercedes Ramirez finds an abused young boy on her porch, covered in blood and clutching a teddy bear, she has no idea that this is just the beginning. He tells her a chilling tale: an angel killed his parents and then brought him here so Mercedes could keep him safe.
His parents weren’t just murdered. It was a slaughter―a rage kill like no one on the Crimes Against Children team had seen before. But they’re going to see it again. An avenging angel is meting out savage justice, and she’s far from through.
One by one, more children arrive at Mercedes’s door with the same horror story. Each one a traumatized survivor of an abusive home. Each one chafing at Mercedes’s own scars from the past. And each one taking its toll on her life and career.
Now, as the investigation draws her deeper into the dark, Mercedes is beginning to fear that if this case doesn’t destroy her, her memories might.