Series arc maybe? I've been wondering what you would call a story line or subplot that extends over several books.
Whatever you call it, Victoria Thompson does a great job in her Gaslight series. Yes, each book is a stand alone mystery--complete with catching the villain. But there are other threads running through the series, compelling you to read just one more book. Who killed Sarah's husband? Will Sarah and Malloy get together? What have Maeve and Catherine been through and what will become of them? And what about Sarah's parents?
I'm not sure if I've spent more time enjoying them or studying them.
It's got me thinking about others who have done that well in books and television. Romances are popular in cozy mysteries. Then there's Monk's search for his wife's killer. The Fugitive's search for the one armed man. In Castle, Kate Beckett is searching for her mother's killer. In Bones, Brennan is looking for the truth about her parents. In Burn Notice, Michael Weston searches for who burned him.
And that's got my wondering what overarching story line(s) I could add for the cozy series I'm querying.
Do you know what to call this device? Do you have any favorite "series arcs" that drew you in?