Maybe Macbeth and Lady Macbeth tried to do it while sleeping? (6)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

A reference to Lady Macbeth’s sleepwalking speech, including the phrase “Out, damned spot!”: she’s trying to wash a stain off her hand, or (whimsically) to DE-SPOT it. A violent tyrannical ruler, such as Macbeth becomes when he finds that one murder leads to several more in an attempt to cover it up.