The Phantom Patrol by James R. Benn

Winter 1944: Months after the Liberation of France, ex-Boston cop Billy Boyle finds himself in a Paris reeling from the carnage it has endured but hopeful that an end to war is in sight. When Billy finds a rare piece of artwork after a tense shoot-out in the Père Lachaise Cemetery, he thinks it could be connected to the Syndicat du Renard, a shadowy network of Nazi sympathizers known to be smuggling stolen artwork out of France.

Trailing the Syndicat, Billy discovers that someone with a high level of communications clearance—someone in the Phantom regiment of the British Army—may be using his position to aid the thieves. Billy, determined to stop the abettor, heads up to the frontlines where he experiences a last-ditch battle against overwhelming odds. There, the ruinous Battle of the Bulge unfurls in the Ardennes Forest. Can Billy and his team survive the bracing onslaught and return the stolen artwork to its rightful protectors?