The most frenzied American ritual you've never seen is called the "transfer of families," a five-hour tsunami of activity that transforms President Obama's home into President Trump's.
"I call it organised chaos," said Gary Walters, who choreographed several transfers of families in his 21 years as the White House chief usher.
"It's energising," said Ann Stock, who saw the transfer up close as the Clintons' social secretary, "but absolutely exhausting."
Here's what happens on Inauguration Day before and during those five hectic hours.
Ready: (Relative) calm before chaos
The 90-plus permanent White House staffers and a few trusted contractors show up around 4am - some sleep on cots at their workstations - ready to execute the battle plan devised by the chief usher. Although this will be Chief Usher Angella Reid's first transition, staff turnover at the residence is rare, so most of these folks have done this at least once before.
The kitchen staffers are among the very few who are not pulled into moving duty, because they are already scrambling to create breakfast, the traditional congressional coffee, afternoon snacks, dinner for who-knows-how-many and preparations for the next day's social events.
(To be clear, we are talking about the residence staff, not the administrative staff. The press secretary does not make the First Family's beds, and policy advisers do not arrange the president's sock drawer. However, they probably will schlep their own boxes to their new offices in the East and West wings.)
Some items for the new family may be stored in out-of-the-way places on the ground floor such as the China Room, and a bit of moving work may begin early and inconspicuously, but no one wants to appear to be shooing the first family out the door.
"We always remember that the house still belongs to the current president up until the time the new person raises their hand and takes the oath," said Reid's immediate predecessor, Stephen Rochon, who was a Coast Guard rear admiral before arriving at the White House. Rochon said residence staffers are ferociously discreet and do not discuss politics - ever.
Set: Getting close ...
About 8.30am, the staff gathers in the State Dining Room to say goodbye to the first family and give them a special gift. During President Ronald Reagan's departure in 1989, Walters, then the chief usher, began a tradition of presenting a box made of historic White House wood that contains the flags that flew over the White House on the president's Inauguration Day and on his last morning in office.
The moment is always bittersweet.
"President Bush was pretty much in tears when he addressed the staff," Rochon said of the younger Bush. "As a retired military officer, I'm not supposed to be tearing up, but I did - and so did the staff."
About an hour later comes the last official event that the outgoing president will attend in the White House, a coffee in the Blue Room that includes the incoming and outgoing vice presidents and their spouses and a congressional escort.
By 10.30am, they will leave through the North Portico, and limousines will carry them to the Capitol.
Go! At 10.31am, cue the crazy
Teams of workers fan out around the residence, but the most intense action occurs in the family living quarters on the second and third floors - and in one key room in the West Wing. The family has (usually) done a lot of packing ahead of time, so the staff boxes up all remaining items.
Truck ballet
The outgoing family's moving trucks, escorted by the Secret Service and officers of the US Park Police, pull into the west side of the South Portico driveway. The incoming president's moving trucks pull into the east side of the South Portico.
Besides moving vans, other trucks carry furniture and artwork to and from the White House warehouse in Maryland, and still others bring on-loan artwork from outside collections and new purchases from furniture stores - all secured by the Secret Service.
Commercial movers may unload their trucks, but that is as far as they get. For security reasons, only residence staffers are allowed to move items into and out of the White House, so electricians, carpenters and many other staffers become temporary movers.
"You don't want a personal item showing up on eBay," Rochon said.
Cleaning, repairing, sprucing up
After the outgoing family's possessions have been removed, housekeepers go into overdrive, thoroughly scrubbing the residence. Rugs and window treatments are cleaned or replaced. "De-petting" will be required, especially if the new family has pet allergies.
Room temperatures and humidity levels are set to the new family's preferences.
Plumbers, carpenters and engineers make small repairs. Electricians may install new light fixtures and run internet and TV cables. Carpenters and the curator's staff hang new artwork. Painters may be called in for touchups.
But no major construction, painting or wallpapering happens on Inauguration Day - there just isn't enough time.
Setting up the bedrooms
The residence has as many as 16 bedrooms, and carpenters may convert suites to separate bedrooms or vice versa by opening or closing existing doors and wall panels. Walters said about half were reconfigured during the Reagan-to-Bush changeover to accommodate the large Bush family.
The new president's interior decorator and a few other members of his entourage help unpack and arrange furniture.
All boxes are emptied, and clothes are placed in closets and drawers. Unlike pretty much everyone else who has ever relocated, the president will not have three unopened moving boxes sitting in the back of a closet.
The First Family's favourite products were purchased ahead of time and will be ready for them to use - everything from mattresses and linens to shower heads and shaving cream. The first family never runs out of toilet paper.
Stocking the rest of the residence
The family has a private kitchen and pantry on the second floor, plus a wet bar and another kitchen on the third floor. President Dwight D. Eisenhower, who spent lots of time in the Solarium, added the third-floor kitchen so that he could make soup without having to carry it upstairs. All the kitchen and pantry spaces are stocked with snacks, drinks and any other food the family has requested. (Fun fact: The president pays his own grocery bill.)
The florist puts fresh arrangements all over the house. The theater is stocked with new movies, the bowling alley gets a supply of new shoes.
Sometimes, the roof terrace is redecorated. Strategically placed plants, for instance, can create more privacy if a certain person were to want to sneak a smoke.
The Oval Office: Staging history
Most parts of the East and West wings are in a state of flux on Inauguration Day as the General Services Administration (GSA), which oversees those office wings, cleans, paints and preps for the new administration's staff. But one room has to be in impeccable shape: the Oval Office.
"That's the first thing the president wants to see," Walters said. "That first impression sends a message to the American people about what's important to this president."
That means every choice may be scrutinized for hidden meaning. A minor hubbub arose when President Obama replaced a bust of Winston Churchill in the Oval Office with a bust of the Rev. Martin Luther King Jr. Donald Trump has said he plans to bring back Britain's wartime prime minister.
The GSA collaborates with the residence staff on this room. Some changeovers require more work than others. During Nixon's inauguration, electricians had to remove a bank of televisions installed by media-obsessed Lyndon Johnson. When Ford took office, he had Nixon's recording equipment and wires torn from within the walls.
All furniture, draperies and artwork will be changed - if the new president chooses to change them. The rug with the presidential seal probably will remain, at least for awhile, because new ones take so long to make.
Sometime before noon, a National Archives and Records Administration crew will sweep through all offices to collect any remaining documents from the old administration, including those on computer hard drives. They also pick up gifts from foreign leaders that may be displayed in the residence.
Last-minute surprises
By about 2.30pm, the inaugural parade has begun, and the chief usher is making sure everything is perfectly in order.
This is often when the unexpected occurs, and the staff has to be ready.
During George H.W. Bush's parade, his twin granddaughters Barbara and Jenna - who would later be White House residents themselves - became bored and wanted to enter the residence, Walters said. So the florist took them to her shop and gave them an impromptu class in floral arranging.
Stock said that during Clinton's inaugural parade, the president felt bad for performers whose floats had broken down, so he invited them back to see his new house. They came the next day, along with thousands more people whom the gregarious president invited along the way, and the guest list swelled to 4500 - triple the number the staff was originally expecting. Storeroom clerks had to scour the city for more hot chocolate to serve.
3.30pm: Deadline
Any time between 3.30 and 5pm, the new first family will return to a transformed White House.
As they enter, usually through the South Portico, Chief Usher Reid will greet them and say for the first time, "Welcome to your new home, Mr President."
The factory had produced 6616 tons of toxic gases by the war's end.