Entertaining but not memorable.
H/h have a history. Seven years prior, they were caught in each other's arms by the heroine's father. The hero refused to marry her to save her reputation. A week lalter, the heroine became engaged to another man.
Seven years later, they both have a different interpretation of the past. The heroine is a widow dealing with her lusty brother in law. The hero is trying to marry off his sister to a rich and titled man capable of taking care of her. The sister is in love with an man she knows her brother will never approve of. She runs to the heroine for sanctuary so that she won't have to return for another London season and spend time with the men her brother has approved.
So the H/h must face each other again after seven years of silence. The attraction is still there. But so is the seven years of hurt, mistrust and animosity.
Spoilers follow:
The biggest problem I had with the story was the hero's reaction when he finds out that the heroine knew his sister was in love with an unsuitable man and didn't tell him. He considers it a betrayal and overreacts, blaming the heroine for his sister's actions (running way to marry the man she loves). In reality, if he had known his sister's feelings, he would have done something drastic to keep her away from the man she loved - because he's a controling male.
The heroine explained that she made the vow to keep the secret before the H/h married and before the hero asked that she never keep any secrets from him. Women have honor, too. Marriage doesn't mean she stops being her own person, or that she has to give over all her connection, commitments and vows to her husband.
All ends well. The hero learns his lesson. They all forgive each other and promise to do better in the future. If this was a real couple, I'd wonder if they could have a happily ever after. Their primary trust issue was not solved (might take a lifetime).