In Ghost Image, the follow-up to 2013’s Multiple Exposure, photojournalist Sophie Medina is working freelance jobs in Washington, DC, while her ex-CIA husband travels abroad as a troubleshooter for a major oil company.

Kevin Boyle, an old friend who is now a Franciscan friar and a controversial environmental scientist, meets with Sophie to discuss one of her photo projects. While they’re together Kevin reveals that he is being stalked, possibly because of a momentous discovery he’s made.

“If I’m right,” he says, “I found something of historical importance that…could be worth a lot of money to the right people.” He refuses to give Sophie the details, not only because he’s still seeking “the last piece of the puzzle,” but also because it’s safer if she doesn’t know.

Soon afterward, Sophie finds her friend lying dead in the garden of his Franciscan monastery. Brother Kevin might have fallen to his death, but after their conversation Sophie has good reason to believe he was pushed.

Sophie comes into possession of a key that leads her to a locker at the Smithsonian National Museum of Natural History where Kevin had hidden a priceless 17th-century botanical encyclopedia. Certain the book is worth killing for, with a value beyond its historical significance, Sophie stashes it in a safe place and launches a personal search for Kevin’s murderer.

As she talks with botanical experts in the U.S. and visits the Millennium Seed Bank in England, she realizes Kevin was trying to track down seeds of a supposedly extinct plant. This plant has miraculous properties that modern pharmaceutical companies would pay millions to obtain. Kevin had a deeply personal interest in the potential cure promised by his discovery, and as it turns out, so does Sophie.

The harassment Kevin experienced shifts to Sophie and becomes increasingly ominous. The wealthy businessman who financed Kevin’s research insists the book belongs to him and Sophie must hand it over. Her every move is being watched, and someone is trying to kill her.

The mystery contains a wealth of historical and botanical information that requires attentive reading, and moves at a leisurely pace until the climactic chapters. The manner in which Sophie acquires the fateful key is unlikely, and as usual in amateur sleuth mysteries, the heroine persists in a dangerous personal investigation instead of taking her suspicions to the police. However, these genre hallmarks are offset by an intriguing premise, a lucid prose style, a likable heroine, and precise characterization.

Crosby makes good use of sites in Washington and London, cities she has lived in and knows well, and she brings her settings to life with insider details. She paints a merciless, and all too believable, picture of self-important types like the senator who suggests Sophie forgo a fee in exchange for the honor of photographing her daughter’s wedding to an Austrian archduke.

“Do you realize how much publicity you’re going to get just from being chosen as the photographer for this wedding?” the offended senator says when Sophie demurs. “A royal wedding in Washington? You couldn’t pay for that kind of exposure.” Every reader will like Sophie for refusing to give in to this nonsense.

Ghost Image should appeal to history buffs and to anyone who is concerned that modern society, with its focus on a chemical solution for every problem, might be overlooking or destroying the natural plant life that could save us from deadly diseases.

Sandra Parshall is the author of the Rachel Goddard mystery novels. She lives in Northern Virginia.