When a distracted single mother learns her seemingly innocent 14-year-old son has live-streamed his murder of a girl, she must prove he is not to blame, but instead she uncovers an insidious challenge game, and his possession by a fusion of a murdered boy and her son’s primordial obsession.

Please clean up your syntax.

Why is the mother "distracted?" I am curious to know what her flaw is. (I put "guilt-ridden" but you are the one calling the shots.)

When she watches an online video of her teenage son murdering a girl, a guilt-ridden single mother must ...

What, what, what can or must she do???

As Richiev has pointed out, how can she prove he is not to blame if there is actual proof of him killing someone? Even if he were forced or tricked into it, the fact that he has killed is a heavy stone.

In any case, the second half of the logline makes little sense?syntactically, too. Which brings me to the beginning of this comment:

Please clean up your syntax.

Her son is a murderer. Why should the audience care that the mom wants to prove that, "he is the real victim" Just curious?