From an Unknown Sender — Traci Hunter Abramson

After spending a busy holiday season putting drug smugglers behind bars, CIA operative Cole Bridger is looking forward to spending a quiet Christmas in Vienna with his girlfriend and fellow operative, Isabelle Roberts. But when Isabelle is tasked with investigating a string of suspect financial transactions and redirects a suspicious package to a museum in Amsterdam, she inadvertently places Cole’s cousins in the crosshairs of a drug smuggling ring. Lars and Marit have no desire to be drawn into the deadly dealings of the criminal underworld, but when Lars’s sister, Tess’s, life is placed in danger, they willingly join Cole and Isabelle in their efforts to uncover the mastermind behind the drug smuggling ring. Unfortunately, the two couples’ involvement does not go unnoticed. And though each step brings them closer to the truth, they also reveal a startling picture of greed and corruption at the center of a dangerous organization that will stop at nothing to retrieve what it has lost.