#38 The Queen of Hearts by Kimmery Martin

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Zadie Anson and Emma Colley have been best friends since their early twenties, when they first began navigating serious romantic relationships amid the intensity of medical school. Now they're happily married wives and mothers with successful careers--Zadie as a pediatric cardiologist and Emma as a trauma surgeon. Their lives in Charlotte, North Carolina are chaotic but fulfilling, until the return of a former colleague unearths a secret one of them has been harboring for years

I always like a good female friendship book. But the mystery here didn't fully make sense.