A Whisper at Midnight by Darcy Burke

Private investigator Matilda Wren’s new client is a woman seeking evidence to divorce her husband. She is also the former fiancée of her last client—and dear friend—Lord Ravenhurst. Though he has enthusiastically offered to aid Tilda with future investigations, she can’t very well accept his help in this matter. Especially when her client’s husband is murdered, and Ravenhurst is a suspect.
Hadrian Becket, Earl of Ravenhurst has never felt more alive than when he was solving a mystery with Miss Wren, even when suffering headaches from using his newly acquired ability to touch an object and see a person’s memories. He wants nothing more than to continue their professional association as well as deepen their friendship. Except now he must prove he isn’t guilty of murder, even if that includes working against his former partner.
Tilda can’t believe Hadrian is capable of harming anyone, but how well does she know him? She must rely on her intellect and investigative skill—and not allow her affinity for him to cloud her judgment. When the killer strikes again, Tilda sees that the danger is not to their friendship after all, but to their very existence.