Harriet Bailey's job as a veterinarian often means reassuring pet owners about their adored animals. So, when a local resident is distraught over her missing cat, Harriet does her best to calm the woman's frayed nerves, advising her to wait a bit to see if the cat returns on her own. However, the arrival of a mysterious envelope containing a ransom note immediately proves Harriet wrong. Someone has taken Nessie!

As Harriet investigates, she discovers that Nessie is the subject of her late grandad's most valuable painting, due to the highly publicized story of how Old Doc Bailey rescued and rehomed her as a kitten. When more pets are nabbed, Harriet redoubles her efforts to find the thief. In her search for answers, she discovers old tape recordings of her grandad sharing the stories behind his artwork. Could Old Doc Bailey's own words about Nessie be the key to reuniting the famous feline and the other animals with their families?