About midway through Ray Allen’s book, as he’s spinning tales about the back-biting that unfolded near the end of his tenure in Milwaukee in 2002, he makes an observation that might come as a surprise to those who have never lived the day-to-day of NBA life, but one that becomes a unifying thread throughout the story Allen tells: “The locker room is like high school sometimes, with the cliques that form and the gossip, much of it untrue, that somebody spreads.”

As much as "From the Outside: My Journey through Life and the Game I Love," now available on Amazon (and written with Michael Arkush), is the story of Allen’s rise to basketball greatness, what will grip fans of the NBA is Allen’s recollections of the tumult and drama that unfolded in each of his basketball stops, none so much as in Boston. It’s still pertinent, because even in retirement, the swirl of controversy around Allen — the high-school-level cliques and gossip — remains.

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Just last month, with the Celtics retiring the jersey of forward Paul Pierce at TD Garden, Allen pointedly decided to stay away, instead posting a social-media photo of him golfing. It’s been 10 years since Allen helped Pierce and teammate Kevin Garnett, as part of the "Big Three," win a championship in Boston. But Allen apparently still worries that there’s too much bitterness left between he and Garnett — as well as point guard Rajon Rondo — stemming from Allen’s decision to leave Boston to finish his career in Miami in 2012.

As Allen tells it, there were early signs that he and Garnett, who were both intense players and intense personalities, would eventually clash. Allen recalled dribbling in front of his locker during the Celtics’ preseason trip to Rome in 2007, which was something Allen had done to prepare for games his entire career. The dribbling annoyed Garnett, though, who told Allen, “No, you’re not going to do that.”

“You can’t tell me what to do,” Allen remembered responding, as teammates looked on. “You do what you do, and I do what I do.”

As Allen wrote, “Gee, can two grown men be any more juvenile?” And it was a similar experience when, before the start of the season, Garnett and Allen went out to dinner at a steakhouse in Boston and spoke about their roots together as teenage players in the 1990s, and the pain of being on losing teams in the past. After dinner, Allen wrote, he asked the waitress for the check.

“No,” Garnett said, “I tip way better than him, so you better give me the check.” It was the first time they’d gone to dinner together, and Allen pointed out that Garnett had no idea how much Allen tipped. “There was no point in arguing with the guy,” Allen writes. “What struck me was that he felt the need to be seen as being superior to me, even in something as petty as this.”

It came as little surprise, then, that when Allen left Boston to sign with the Heat, Garnett refused to shake his hand when the two teams met on opening night the following season.

“KG would quarrel with his grandmother if she signed with another team,” Allen said.

Still, Allen wrote that of all the teammates he has had, “If I had to choose only one to play with, it would be Kevin Garnett. No one else comes close.”

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At the opposite end of that spectrum is Rondo. Allen describes their early relationship as one of young player and mentor. “I couldn’t have gotten along with him any better,” Allen writes. “He was like a little brother to me.”

But the relationship unraveled after the Celtics’ 2008 championship. Even with the passage of time, Allen still seems at a loss to explain why, exactly, the dynamic between he and Rondo collapsed.

But by 2011, that relationship was in tatters. Allen recalled that in 2009, because the Celtics’ front office had issues with Rondo, there was talk that Allen and Rondo would be traded to Phoenix for a package built around Amar'e Stoudemire. Allen told Rondo at the time that he should talk to team president Danny Ainge to work out their problems and keep from being traded.

It came up again during the 2010-11 season. In a team meeting, Allen writes, Rondo told his teammates, “I carried all of you to the championship in 2008.”

Allen continued: “The rest of the team, almost in unison, responded, ‘You what?’” Rondo said everyone on the team had problems with him, and when Allen told him, “None of us had issues with you,” Rondo said to him, “You did, too. You told me I was the reason we were going to be traded.”

Perhaps that’s where the problem started, then. In the book, Allen seems genuinely unsure of why Rondo turned on him so completely. Allen describes Rondo as a player who expected that he would be treated as a leader without having done the work to deserve the role, and describes the Celtics as an organization that could not figure out how to handle Rondo. Coach Doc Rivers asked Garnett and Allen to “let [Rondo] into the circle,” but Allen told Rivers, “We can’t make him a leader, Doc. He has to earn it.”

Allen details the famed incident during the Celtics’ playoff series against Miami in 2011, when Rivers was going over film with the team and pointing out some of the errors made during their losses in the first two games. Rondo “put his head down and turned his chair toward the lockers.” Rivers implored him to watch the film.

“F— that film,” Rondo said, according to Allen, hurling a water bottle at the screen and breaking it. Rivers ordered Rondo out. Garnett followed him and said, “Young fella, you need to get your s— together.”

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Before the start of the 2011-12 season, during the NBA’s lockout, there were discussions that Rondo would be traded to New Orleans for Chris Paul, but the possibility of a deal fell through, according to reports at the time, because Paul would not commit to signing with Boston when he became a free agent the following summer.

According to Allen, though, the deal fell through for a different reason: “In the end, Doc decided he couldn’t do that to their coach, Monty Williams. Doc was a mentor to Monty, having coached him in Orlando.”

Once that trade was off the table, Allen wrote that he was shocked to find the Celtics move in the opposite direction — instead of trading Rondo, Rivers decided to build the offense around him, as if rewarding his bad behavior. Allen said the season that followed, “my last under contract, was the most stressful by far. It got to the point that Rondo would not even throw the ball to me.”

That was when Rivers moved Allen to the bench and started Avery Bradley alongside Rondo, and when Ainge nearly traded Allen to Memphis for O.J. Mayo, a deal that was so close to completion that Ainge called Allen and told him it was happening. But it fell through just before the deadline.

The tension within the Celtics came to a peak during a game in Indiana in April 2012. Pierce and forward Brandon Bass had been bickering on the court during the game, and the argument spilled over to the locker room. When Rivers intervened to talk to the team as a whole, Rondo blurted out something about Allen, which led to their own locker-room shouting match.

Rondo claimed Allen was jealous of him, and when Allen responded that Rondo needed to “stop bulls—ing everyone on the team,” Rondo told him, “I’m going to get your ass out of here this summer.” Later, on the team plane, Allen said he approached Rondo to see if the problem could be handled and the hatchet buried. Instead, Rondo turned a cold shoulder and said, “I got 11 games to play with you, and that’s it.”

Of course, Allen did leave that summer, and it was that decision that has left such a wide rift between him and Garnett — Allen patched things up with Pierce last summer, and the Rondo animosity may never subside. Despite the tension of the 2011-12 season, Allen wrote that “The plan was to stay in Boston.” But the Celtics, who signed guard Jason Terry, offered two years and $12 million where Allen was seeking three years and $24 million. According to Allen, the sum total of events in Boston nudged him to sign elsewhere.

“So let me see if I got this straight,” he wrote. “You want to pay me less money. You want to bring me off the bench. You want to continue to run the offense around Rondo. Now tell me again exactly why I would want to sign this contract?”

In the end, Allen took even less money to sign with Miami for two years and $6 million, because the Heat had the best chance to win a title.

“I knew fans in New England wouldn’t be happy with my decision,” Allen wrote, “but I never could have imagined the degree of unhappiness. They acted as if I was Benedict Arnold... My sin was that I had the nerve to leave on my own.”

Indeed, Allen’s account of his time in Boston — and his departure — is fascinating, and highlights his retelling of his journey through rough times in Milwaukee with coach George Karl, his stint in Seattle and subsequent trade to Boston, and the two years he spent helping Miami to the NBA Finals. He is, of course, a surefire Hall of Famer, and has always been a thoughtful and intelligent locker-room presence.

But in the NBA, even the thoughtful are subject to the high-school vibe of a locker room. And Allen’s book gives readers a juicy inside look.