Barbara Michaels/Elizabeth Peters writes witty, suspenseful, romantic mysteries. Some are definitely modern Gothic. Others, like the Amelia Peabody series, are historical. If you like her novels, you might try:

Charlotte McLeod/Ailsa Craig
Laurie King (the Mary Russell and Sherlock Holmes series that starts with The Beekeeper’s Apprentice)
Mary Stewart Her books are classics in the genre of romantic suspense
Joan Smith (as well as her famous regencies, she wrote a handful of breezy, contemporary romantic suspense)
Carla Neggers (although she and other Mira authors are darker edged than Elizabeth Peters). In this darker vein, you could also try Kay Hooper, Tami Hoag, Meg O’Brien, etc.
Janet Neel’s Ticket to Ride isn’t quite romantic suspense. It’s a thriller, a political gothic where the competent heroine is nonetheless vulnerable.