Mackenzie Stewart shoved a flannel shirt into her backpack with more force than was necessary. She had the air-conditioning turned up, but she was hot – hot and agitated and in no mood to have Nate Winter, perhaps the most observant man on the planet, in her kitchen with her.

Although it wasn’t technically her kitchen.

She was a temporary resident in a corner of a historic 1850s house in Arlington. Nate’s archaeologist wife, Sarah, was in charge of getting it open to the public, a task apparently fraught with twists, turns and setbacks. Just when she thought everything was under control, the place sprang unexpected, unexplained massive leaks. Some people were convinced the leaks were the work of the ghosts of Abraham Lincoln and Robert E. Lee, long-rumored to haunt the house. Mackenzie didn’t believe in ghosts. She blamed worn-out plumbing.

Nate and Sarah, pregnant with their first child, had moved into a house of their own in the spring. Sarah had offered the caretaker’s quarters to Mackenzie when she arrived in Washington six weeks ago. While she looked for a place of her own, Mackenzie could be a presence at the historic house, discouraging ghosts and potential vandals, and staying alert for new leaks.

She zipped up her backpack. She was in shorts, but was still hot. “Nate, did you and Sarah ever encounter Abe and Bobby E. while you were living here?”

Sitting at the small kitchen table, Nate watched her with a level of scrutiny that got to most people. He was a feet-flat-on-the-floor senior deputy marshal, tall, lean and notoriously impatient. He, too, was from Cold Ridge, New Hampshire, and Mackenzie had known him all her life. He was like the big brother she’d never had, and he didn’t scare her.