Return to Christmas by Anne Stuart

Madison Simcoe has had enough. She’s a cold, lonely workaholic who’s been harassed one too many times by a fellow worker, it’s Christmas and the spirit is gone, and she feels like a stranger in her own life. A little retail therapy should cheer her up.
Macy’s is huge, a giant store full of wonders, and Madison’s happy place. So when she decides to indulge herself, pushing through the big doors on a cold afternoon in December, she’s not expecting to suddenly find herself in 1947, unable to leave the huge building. And she’s certainly not expecting to find incredibly hot Johnny Larsen, former Army spy during WWII, with a buttload of PTSD, artistic brilliance, and bad attitude, looking out for her.
Bad things happen, even at Christmas, but there’s magic in the air, and Madison is inconveniently in love with a man who must be long dead. Surely there’s a happy ending among the mistletoe and holly?