The Wedding Challenge by Candace Camp

Lady Calandra should have suitors beating down her door. But her overprotective brother, the Duke of Rochford, has managed to scare off every suitable gentleman. Every man except the mysterious Earl of Bromwell, that is. Callie finds herself drawn to the enigmatic earl, despite her brother’s almost violent protestations.

In defiance of her brother’s wishes, Callie devises a plan to see Bromwell again, enlisting the help of matchmaker Francesca Haughston. But when shadowy secrets about the duke and the earl come to light, it may be too late for Callie to see that she’s walked straight into a trap.