A disgraced cop, offered the chance to regain custody of his son unearths a hidden layer of secrets of those involved within and outside the law when he must catch a serial killer before more children die.

I like the idea of your story but felt the logline could do with a bit more work. Here's a rewrite for your consideration. Use it as your own if it suits your story.

"Despite risk of becoming the scapegoat of a corrupt police force, an honest cop commits unwarranted intervention against a child killer thus hindering his chance of regaining custody of his son."