After having fallen in love with Emily The Strange from a graphic novel I serendipitously happened upon at the worshipful local library, I discovered that there was a series of four novels on this same charming deviant, and I requested all four.
In this, the third volume, which was the first I read in order, Emily perfects her Time Out Machine and is able to travel back to 1790 to investigate the demise of a distant relative, Lily, who apparently dies at the tender age of thirteen, at the hands of a 'Dark Girl'. Emily herself is a Dark Girl as was Lily, and so Emily is rather curious as to why one of them would kill one of her own, and wondering if she can somehow change history by preventing the death, and whether such a change would backfire and change Emily's own future so much that she would regret this intervention.
Once again she runs into her nemesis in the form of one of his ancestors, who are just as designing as he is in Emily's own time. She has to figure out why the supply of Black Rock (curiously the name of a location near my home town!) has dried up, and how it can be be set free again. Meanwhile the villain is holding Emily's ancestors prisoner to force them to confess the secret of the Black Rock so they can take it over. Apparently this fight for control of the substance takes place every thirteen generations - which happens to be Emily's favorite number.
And once again Emily is victorious. Those primitive 1790's locks cannot hold her in! Despite a few hair-raising scrapes which actually don't raise Emily's thick, dark locks, and despite at one point thinking she is trapped in the past, she wins through and all is well. A great story!