Romantic suspense weaves a love story through a thriller or mystery plot. The romance and the danger aren't separate tracks; they're interdependent. The romantic interest might be a suspect, a protector, or a fellow investigator. The suspense raises the stakes on the romance (will they survive to be together?), and the romance raises the stakes on the suspense (the hero has something personal to lose).
Romantic suspense is one of romance's most commercially consistent subgenres. It teaches you to braid two arcs together so tightly that neither can be removed without collapsing the other. That structural skill transfers to any genre where you're running dual plotlines.
A woman in hiding and the small-town police chief who threatens to uncover her secrets, classic RS executed by a master.
While not marketed as romance, the Reacher formula (action, attraction, resolution) mirrors romantic suspense structure.
Write a scene where two characters are attracted to each other while also in physical danger. The conversation should carry both subtext (the attraction) and text (the immediate threat). Neither element should pause for the other.