A few years ago I attended a workshop run by Marina Oliver at a Romantic Novelists conference on writing a synopsis. Marina knows what's what. She does quite a few workshops and she has written several books about writing, as well as being an author herself. I think writing a synopsis is really hard, so each time I like to use teaching notes as an outline in the hope that eventually I'll get the hang of how it is done.
Marina advises writing down some basic information first - title, genre, theme, name of heroine, significant facts about the heroine such as her aims, the name of the hero and some significant facts about the hero such as his background. From this you can work up a first sentence. One good tip is to always write the synopsis in the style of your book.
The Glass Cliff is a contemporary horror story set in the industrial north.
Well, I've spent all morning wrestling with what comes next. I think I need to go back to Blake Snyder's Beat Sheet and see if that helps.