An awful and stupid plot saved by compelling central performance

Rating: 4/10 (14 June 2018)

Another film that insults one's intelligence by disguising a ridiculous plot with a fine central performance and slick editing. I had really hoped this film would live up to its hype, but it did not and I sat watching in a state of increasingly disbelief. Spoiler alert - stop reading now unless you want to as my questions will (probably) ruin the film for you.
Why would a poor person undertake to spend $60,000 to rent 3 billboards for a year?
Why would an unknown stranger then pay one month's rental?
Willoughby would never pay another month's rental and his suicide added nothing.
Why attack the dentist?
Why would Peter Dinklage's character lie to provide an alibi?
How stupid is Willoughby if he does not know that Mildred Hays torched the police station? Perhaps they were that stupid and that is reason the daughter's rape & murder had not been solved.
How stupid does Mildred have to be to burn down the one place that has the records of her daughter's murder?
Why have Davis save the (tiny) file detailing the daughter's murder and then do nothing with this twist?
Why would David attack Red Welby? All he had done was rent the billboards.
How unbelievable was the scene with the stranger coming to where Mildred worked?
Off the scale unbelievable was the same man then winds up in a bar talking about his crimes.
Very lame having the stranger's DNA leading to a big fat nothing.
How likely is it that Mildred would team up with Davis to go a 'murdering?
We learned almost nothing and the mystery of the daughter's rape and murder remained.
All in all a hugely frustrating film. I gave it a generous 4 stars because it was compellingly done. However for the awful plot I would want to give it a negative score