Satan's Pony — Robin Hathaway

Hathaway's likeable young doctor, Jo Banks, is solidly ensconced as "house doctor" to a group of motels in the New Jersey countryside. Then one day the motel where Jo is living and where she has her office is suddenly over run by a loud group of motorcyclists. When one of the riders is murdered, suspicion falls on Dr. Jo's landlord's son, who turned up after having been presumed either to have permanently gone AWOL or to be lost in battle in Vietnam. Trying to help her friends, and prove that the man is innocent, Jo takes on a lot more than she may be able to handle.