Series numeration from www.goodreads.com.

"San Francisco book-restoration expert Brooklyn Wainwright and her hunky security-expert husband, Derek Stone, face a locked-room murder mystery during the holidays in Scotland. In the middle of a wonderful Christmas holiday in Dharma, Brooklyn and Derek receive a frantic phone call from their dear friend Claire in Loch Ness, Scotland. The laird of the castle, Cameron MacKinnon, has just proposed to her! They plan to be married on New Year's Day, and they want Derek and Brooklyn to be their witnesses. And while they're visiting, Claire hopes that Brooklyn will be able to solve a little mystery that's occurred in the castle library--twelve very rare, very important books have gone missing. Once in Scotland, Brooklyn starts working on the mystery of the missing books but is soon distracted by all of the thumping and bumping noises she's been hearing in the middle of the night. You'd think the Ghost of Christmas Past had taken up residence. But when one of the guests is poisoned and another is killed by an arrow through the heart, Brooklyn and Derek know this is not the work of any ghost. Now they must race to find a killer and a book thief before another murder occurs and their friends' bright and happy future turns dark and deadly"--,Provided by publisher.