A failed detective’s visitations from the apparition of his comically repugnant deaf mother inveigle him to confront his flaws. He must transform to understand her true demise or his family will implode.

I like the thought that the mother might be a hallucination.

If that is the case. I would add that the mother is a hallucination if it is known to the reader from the beginning, I would withhold that the mother is a hallucination, if that information is a big reveal.

Consider the following:
What’s the connecting tissue of “failed” to his flawed arc?
The use of “comically repugnant” doesn’t translate your premise as comedy to me. Are you shooting for an Andrew Dice Clay persona for the mom? Try a laymen’s term to quickly build this picture in the reader's mind - can a deaf person be “foul-mouthed”?
Keep his ghostly visitations a mystery concerning your reply.
A detective seeking to uncover his mother's death is enough. The “imploding family” part only muddies the waters. If keeping, you’ll have to elaborate as she’s passed – how is this affecting their lives?

Hope you find this constructive, keep going!

Thanks Richiev. I wanted to get over that this is a comedy-drama hence the description of his mother as comically repugnant. The adjectives you've suggested don't really fit with the mother character I have in mind. I'm thinking the mother character may be an hallucination caused by him overdosing on anti-depressants so am wondering whether to change 'visitations from the apparition' to hallucinations.