CHARLOTTESVILLE, Va.

The members of the 2:20 tour follow their guide up the front steps of Monticello, past those iconic white pillars and into the domed building’s aura of wonder. The wooden floor creaks like the knees of an aged host rising from his seat to explain a few things.

The guide speaks in present tense of the home’s most famous occupant  Mr. Jefferson, as he is often referred to around here  while leading the tour into the family sitting room, where his daughter Martha supervised the slaves who worked as household servants.

And there it is again, the great American complication: Mr. Jefferson, who rocked civilization with passionate words about inalienable rights for all, also owned hundreds of slaves.

The guide, Liz Tidwell, who became so enthralled with Monticello that she left Texas years ago to be near it, segues to the And That’s Not All moment. You may have heard of a Monticello slave named Sally Hemings, she says, and of the “great controversy” about a relationship between Mr. Jefferson and Ms. Hemings.