Okay, "The Draughtsman's Contract" - WTF was THAT ending?!

So, I just finished watching "The Draughtsman's Contract" and... I'm so confused but kinda fascinated? Like, the whole time I was watching, I was trying to figure out what the deal was. All those powdered wigs and fancy clothes just felt so...extra. But in a good way, I guess? It's so stylised and visually interesting, I couldn't look away, even when I didn't totally get what was happening. That said, seriously, WHAT was with the ending?? All those drawings and clues, and then BAM, murder! I was expecting some kind of grand reveal about the affair, or some secret political conspiracy, but it just kinda spiralled into chaos. Did the draughtsman (which, btw, is a super weird job description lol) actually kill him? Or was he just framed? And who was the dude in the black mask at the very end? I NEED ANSWERS! And okay, let's talk about Sarah Miles' character. That Mrs. Herbert was totally playing games, right? She was so cold and calculating, I couldn't tell if I should root for her or be completely creeped out. She seemed to be manipulating everyone, but what was her end game? I feel like I missed a bunch of subtext. Help me unpack this, people! I don't want to have wasted almost 2 hours staring at some rich people's lawn ornaments without understanding something profound.