Working out 'who done it?' Grappling with plot outlines

My wrists ache, my shoulders are sore, my brain has been spinning all night and I feel guilty because I didn't e mail or phone any of my friends yesterday. I barely looked at Facebook and Twitter, and my husband got about half a dozen words out of me - which might be a blessing, of course, as far as he's concerned. Why? Because I was grappling with the plot of the next DI Horton marine mystery crime novel, and couldn't for the life of me fathom out who had done it!

That might sound weird, as I'm the author, surely I should know, but this often happens. I had reached the climax of the novel with its sub plots and main plot and had several suspects in the frame, then I started to think, 'No, it's too obvious it's him,' or 'It can't be her because she's got no motive.' I could, of course, invent motives aplenty, but it's got to ring true. Now, after bashing out a sketchy end on my keyboard yesterday evening, considering it overnight and looking at it in the fresh light of day, I believe it will work. I hope it will work. Yes, I'm sure it will work and give my readers something to get their teeth into. Only the next revision, which I shall start today, will prove whether or not I'm right.