In S. C. Perkins's Lineage Most Lethal, the captivating second mystery in the Ancestry Detective series, Texas genealogist Lucy Lancaster grapples with a mystery rooted in World War II and espionage.

It's the week before New Year's Eve and genealogist Lucy Lancaster is ready to mix work and play at the beautiful Hotel Sutton, enjoying herself while finalizing the presentation for her latest client, hotel heiress Pippa Sutton.

Freshly arrived at the hotel—and determined not to think about Special Agent Ben Turner, who went radio silent on her after one date—Lucy is stopped in her tracks when a strange man comes staggering toward her. She barely has time to notice his weak, sweaty appearance before he presses a classic Montblanc pen onto her hand, gasps, "Keep them safe," and collapses at her feet, dead.

When Lucy shows the fountain pen to her grandfather, an avid collector and World War II veteran, she's in for another shock. Not only does Grandpa recognize the Montblanc, he also reveals a secret: he was an Allied spy during the war and the pen is both a message regarding one of his wartime missions and the key to reading a microdot left by the dead man.

On the microdot is a series of ciphers, some decrypted to form names. Could they be the descendants of Grandpa's fellow spies? When two from the list end up murdered—including the chef at the Hotel Sutton—and Grandpa's life is put in jeopardy, Lucy's sure she's right. And with Lucy's and Pippa's names possibly on the list, too, she's got to uncover the past to protect those in the present.

With a secret Allied mission, old grievances, and traitors hiding behind every corner, Lucy must use her research skills to trace the list's World War II ancestors and connect the dots to find a killer in their midst—a killer who's determined to make sure some lineages end once and for all.