The More the Terrier by Linda O. Johnston.
You've heard of hoarders? You know those people who obsessively gather STUFF until their homes are hazardous mazes of clutter? According to the Mayo Clinic, "[s]ome people also collect animals, keeping dozens or hundreds of pets often in unsanitary conditions".
This is what Lauren Vancouver, manager of a private, no-kill animal shelter discovers when she visits her old friend and mentor Mamie Spelling after receiving a panicked call from her. Mamie is afraid of Bethany Urber, the ambitious and aggressive CEO of a shelter network, who threatened the older woman when she refused to join the network.
Lauren feels that the only thing she can do is contact Animal Services, who move the animals to their own shelters, and arrange for psychological evaluation for Mamie.
Shortly after Mamie is released, Bethany is found in her office, shot. Unfortunately, Mamie finds the body, and having vocally castigated her in public, she becomes the main suspect.
Lauren is aware that Mamie is unstable, but still certain that her friend is incapable of murder, and takes it upon herself to prove it.
With the Pet Rescue series, Johnston has found a palatable way of conveying information about issues that are unpleasant but very real. (The first installment of the series was about another serious problem, puppy mills.)
Linda O. Johnston also writes the Kendra Ballantyne, Pet-Sitter mysteries. She volunteers at no-kill shelters in Southern California, and become a dog adoption counselor.
*FTC Full Disclosure: Many thanks to the publisher, who sent me a copy of the book for review purposes.