"We do not touch the bag."
This was the warning Capricia Penavic Marshall, then the chief of protocol for the United States, was told by a palace official when she stepped forward to help Queen Elizabeth with her purse during President Barack Obama and First Lady Michelle Obama's visit to Buckingham Palace in 2011.
Marshall was immediately apologetic after the polite correction. But she also wondered: What was in Her Majesty's bag?
Marshall, who previously served as social secretary during the Clinton administration, was accustomed to offering to take women's bags during official moments. So when the Queen, 94, was about to step out to the palace lawn for the arrival ceremony for the Obamas, the protocol chief made a slight move forward.
"As Her Majesty walked out, I made a comment to my counterpart. I said, 'Oh, my goodness, Her Majesty has her bag.' And I made an ever so slight move with my left foot," Marshall, 56, recalls during an exclusive interview with PEOPLE about her book, Protocol: The Power of Diplomacy and How to Make It Work for You, which released on Tuesday.
"He, with both of his hands, pushed me back against the wall and said, 'Do not touch the bag.' and I said, 'Oh, my goodness. I'm so sorry,' " Marshall says. "He goes, 'We do not touch the bag.' And I said, 'Okay, I apologize. I would never. But do we know what's in the bag?' And he said, 'We don't know what's in the bag. But we never touch the bag.' "
While Marshall is an expert in the diplomatic art of etiquette, she is always open to learning more — especially about the Queen of England.
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"I did learn later on that she perhaps uses the bag as a signal," Marshall says now. "If it's on one part of her arm, it means the meeting is going fine, leave me alone. But if she lowers it, it means, 'End this now. I want to go.' People have speculated that in the bag, she has a cell phone so that she can call and speak to her grandchildren, which I just absolutely adore."
Marshall's interaction with palace staffers is just one of many fun, anxiety-inducing and inspiring anecdotes she shares in her book about her 12 years in the White House.
Her hope is that her memories and advice together provide guidance so that anyone — from government officials to parents on a parent-teacher conference call — can improve relationships by communicating with care and purpose.
"My job was to elevate our diplomatic engagements when the leaders of my country were working with others at the very highest levels. They were trying to navigate their foreign policy differences and come to some sort of agreement," she explains of the importance of protocol. "My hope is that people will see that there is this magical tool out there that, unbeknownst to them, could shift their negotiations. It could pivot the power to their advantage."
Marshall writes in Protocol about the ways that a room's decorations and lighting and even the hanging of a flag or the grip in a handshake can positively or negatively impact the progress of a meeting.
She also explains the power of gift giving, which came into play during an exchange between the Obamas and the royal family in 2011.
After the delegation luncheon, she explains, the Queen wanted to exchange gifts with the president and first lady. ("She truly almost acts like her own chief of protocol," Marshall says of the monarch. "She's been doing this for so very long.")
"We wanted to make sure that what we were furthering this special relationship with the U.K. and particularly with Her Majesty," Marshall says. "President and Mrs. Obama were so, so very fond of her. In doing our research, we learned that [Queen Elizabeth] had a cherished relationship with her father, and she collected anything and everything that she could about him."
Marshall and her team put together a collection of memorabilia from King George VI's last visit to the United States, including invitations and notes, which were put into a leather portfolio.
"When she walked over and she's flipping and looking through the pages, I'm looking at her and I'm like, 'Oh, goodness, I hope that she likes it,' " Marshall tells PEOPLE. "And I want to say that I saw a little glisten of a tear in her eye after she paged through it a bit. She looked to the president said, 'Thank you so very much for this.' "
President and Mrs. Obama also gave Queen Elizabeth a floral brooch, which she loved so much that she wore it during President Donald Trump's state visit to the United Kingdom in 2019, according to Marshall's book.
She says one can only guess at the Queen's reasons for wearing that specific brooch for that specific Trump trip.
"I'd like to say that she was proud to wear a piece of a presidential gift and was displaying the unity between the two nations," Marshall says. "I think that she has the capacity to always lift the message up right now and to create those stronger bounds. But she herself is the only one who will really know."
Beyond her time in London, Marshall also describes important visits with heads of state, multiple trips across the world and personal moments with the Obamas and Clintons — all of whom she admires.
"They are two of the best jobs I've ever had in my life," she says of working for the first couples.
"I learned a great deal from their leadership traits, each of them very different. President Clinton has a wonderful desire to engage and is curious about people. And his curiosity of difference of background really stayed with me," she says. "All four of them share in that great trait ... Many people think that when you are leadership that you have to convey decisiveness and strength to be a good leader. I had found through my experience with them that it really was their empathetic style of leadership that was most effective."
She says that President Obama has a "wonderful sense of humor" and she considers Secretary Clinton a mentor.
"When you're a young person who is trying to figure out your path, and when she stepped in and she offered that guiding hand — it certainly was unexpected and ever so welcome," Marshall says. "And I have to say that my career would not be anywhere near what it is today if she hadn't done so."
Secretary Clinton has also shown support for Marshall's latest endeavor.
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"Protocol is a must-read, taking us behind the curtain of the highest levels of diplomacy, teaching us lessons about the intersection of governing and humanity that we need now more than ever," the former first lady, 72, said in a review of the book.
While Protocol doesn't specifically address President Trump, who often tweets insults at his enemies and has become known for his aggressive style of handshake, Marshall did address the consequences of his divisive communication style.
"Protocol is completely about connecting through empathy and humility and persuading through preparation. When you have a lack in those areas, you are doing yourself a disservice in your ultimate goals," she says.
"With each new inhabitant of the office of the presidency will come their skill set and understanding of how to either effectively use these tools to their advantage and to the country's advantage, or not," Marshall continues. "The way that they conduct themselves, does it achieve their ultimate goal? And I think that's the telltale [sign] in the end is if the goal is achieved through the means that are used."
Protocol is on sale now.