Sean Lennon can pinpoint the exact moment when Primus warped his brain. He was 15 and in the process of moving back to New York from Switzerland, where he studied at an elite boarding school near Rolle. While walking the streets of a small, sleepy, rural Italian town with a girl he was dating, he heard this unusual, loud music bumping at a small club near an empty street corner.

“Everything else in the town was closed, so we walked in,” Lennon reminisces a quarter-century later from his Upstate New York studio, where he’s currently working with the Black Lips. “The entire place was jumping up and down— vibrating—like this little shack that was dancing. The guy I’d later know to be Les Claypool had these multicolor dreads with shaved hair on one side. He was doing this weird crab walk and singing ‘Jerry Was a Racecar Driver.’”

Lennon, the son of John Lennon and Yoko Ono, had tastes that mostly fell on the song-oriented side of the classic-rock spectrum at the time, but that show inspired him to dive into virtuosic instrumentalists like Tony Levin and prog-innovators such as King Crimson, which served as a gateway to the “player-centric, shredder music” that remains close to his heart. In a very real way, it also opened up the rabbit hole that eventually led to his current collaboration with Primus’ distinctive bassist and frontman himself, in their new outfit The Claypool Lennon Delirium.

“Primus wasn’t on MTV yet— they were super underground— and people were hurling themselves from the balconies in the name of moshing,” Lennon says of that initial sighting. “That was the first time I’d seen people violently interacting within a circle of men, athletically chest-pounding. I hadn’t heard of Nirvana or anything that was later to be associated with that kind of behavior.”

So it’s no surprise that when The Ghost of a Saber Tooth Tiger—Lennon’s current psych-rock project with his romantic partner Charlotte Kemp Muhl— was offered an opening spot for the reactivated Primus on their 2015 tour with Dinosaur Jr., Lennon jumped at the opportunity. “I wanted to make another Ghost record after touring for a couple of years, but when we were told we might play with Primus, we were like, ‘Let’s get back out there,’” Lennon gushes. “It was a very special tour—we wound up jamming with Les backstage and he invited me to sit in on ‘Southbound Pachyderm,’ which was pretty much my favorite song.”

Much to Lennon’s delight, when the summer outing wrapped up, Claypool suggested they capture their instant chemistry in the studio. “Primus had been going strong for five years, so it was time to take a year off, and I was trying to fire up the old Oysterhead machine,” Claypool says of his supergroup with Phish’s Trey Anastasio and The Police’s Stewart Copeland, which— with the exception of a one-off appearance at Bonnaroo in 2006—has been dormant since 2001. “The schedules weren’t aligning. So when I was hanging out with Sean on tour, I just said, ‘Hey, I’m looking for new work to do this year. What are you doing?’”

That fall, Lennon shipped out to Claypool’s Marin County, Calif., studio, where the duo hashed out a batch of new, original songs over some pinot noir or, as Claypool playfully explains, “We had more than 10 kids in six weeks.” Though both Claypool and Lennon brought a few sketches to the sessions, they baked up most of the album’s ideas together with the initial goal of making an album of Syd Barrett-influenced psych tunes.

While the resulting collection, which is slated for release in early June as Monolith of Phobos—a very Dark Side-like reference to a mysterious rock structure on a martian moon— certainly nods to early Pink Floyd, the album is a true synthesis of the Delirium’s namesake musicians. The 11-song opus opens with Monolith of Phobos’ title track, a freaky survey of the record’s varied sounds—it begins with a steady drone and eventually moves into a creepy mélange of Claypool’s twisted, cartoonish vocals, and postcards from Lennon’s long association with New York’s art scene and current DIY psych renaissance. From there, the album truly blasts off with the two-part “Cricket and the Genie” suite. “Part I” somehow manages to capture a punishing “War Pigs” march via Tame Impala’s “Elephant,” a neo-classic that looks back on the Black Sabbath chestnut through John Lennon’s kaleidoscopic lens. Meanwhile, “Part II” transposes creepy carnival sounds and guitar wizardry over genie-like vocal loops and, of course, the aforementioned cricket chirps.

In recent years, Lennon has done a remarkable job broadening the network associated with his family act, Plastic Ono Band, by drawing in modern luminaries like Mark Ronson, Peaches, Wilco’s Nels Cline, The Flaming Lips and members of Sonic Youth. Claypool says that he was attracted to Lennon’s “eclectic nature”—which he sees as a mix of Ono’s art-rock curations and the elder Lennon’s pop perfection— from the first time his manager showed him one of Ghost’s YouTube clips. Lennon jumps in, adding: “Les’ music is really in your face and hard-hitting and surreal and provocative and exciting, but he’s also a pretty chilled-out guy.”

The new friends ended up playing all the album’s instruments themselves— Claypool says that, not counting the Robot Chicken soundtrack or a stray theme song, Monolith of Phobos marks the first time he’s had a keyboard credit on a record. “Everything we did is pretty much 50/50,” he says. “I haven’t had that kind of relationship in quite a long time, if ever.” Claypool makes a point to mention that Lennon plays drums on almost all of the album’s tracks. “Normally, I play quite a bit of drums and percussion on my records,” he says, praising Lennon’s “lopey” style numerous times before admitting that his collaborator would probably hate that description of his approach. “His drumming has a totally different feel. My drumming hero is Stewart, and I lean forward on the beat, while he has this style that is like Ringo or Nick Mason.”

The album’s centerpiece, “Boomerang Baby,” is a swirl of fuzzy guitars, harpsichord keys and distinctive Claypool bass slaps. (If there is any question who is supplying the low end on this album, then look no further than the punny “Breath of a Salesman.”) “Captain Lariat” is the best mashup of Claypool and Lennon’s varied approaches— a swirl of Zappa’s classic We’re Only in it for the Money vocal satire, Lennon’s tasty guitar licks and light baritone vocals that will surely explode into a true assault live. And speaking of Pink Floyd’s orbit, Lennon captures a bit of David Gilmour’s soaring, clean, melodic tone on the record’s penultimate track, “Bubbles Burst.”

Lennon admits to being a “little nervous” going into the sessions. “Neither of us knew exactly what we were getting into,” he says. “I did a lot of practicing—trying to get warmed up. I thought that I’d be intimidated playing with Les, but he just really guided me through it in a very generous and easygoing way. Despite his virtuoso accomplishments, he managed to make me feel at ease.”

In terms of The Claypool Lennon Delirium’s development as a formal project, both musicians are adamant that the songwriting sessions were secondary to the bonding that took place outside the studio. “The whole crux of our friendship was that we would sit down and geek out with each other about film and art and literature and music,” Claypool says, noting that he screened The Monkees’ adventure film Head for his slightly younger collaborator for the first time and dissected Chilean director Alejandro Jodorowsky’s influence. Their shared sense of humor clearly rubbed off on the irreverent social commentary “Ohmerica,” which warns that, “If we stop shopping, the terrorists win.” “Sean’s got a very colorful background being around his mom, and his whole life,” Claypool says. “His perspective on things is pretty unique and interesting.”

Claypool and Lennon have blocked off their summers to support Monolith of Phobos during a mammoth tour that will extend into September. (They’ve also already secured some prime fall festival dates.) When it came time to put together a live version of The Claypool Lennon Delirium, the duo assembled an all-star band, featuring Beastie Boys keyboardist Money Mark, who Lennon has known since his early days on Grand Royal, and drummer Paul Baldi of Claypool’s Fungi Band. “For me, it’s particularly about how good a hang somebody is, and I’ve heard from a few people— and known from the few times I’ve met Mark—that he’s a great guy,” Claypool says with a smirk.

Baldi entered the fold after Claypool and Lennon went to see Black Sabbath at New York’s Madison Square Garden on another wilderness-like bonding outing after the sessions wrapped.

The bassist was struck both by their setlist—which leaned almost entirely on the quartet’s ‘70s prime—and the absence of their original drummer. “We toured with Sabbath when they had Bill Ward on drums,” Claypool reminisces about Primus’ stint on Ozzfest in the ‘90s. “This new guy was spectacular, but there was something about seeing them with Bill that was unbelievable because he has that kind of lopey feel— he slows it down. It’s an interesting feel that you don’t see in my world very often. So I suggested getting Paulo.”

The music that Claypool and Lennon recorded in the laboratory clocks in at just north of 50 minutes, so they plan to spike their sets with material from their individual catalogs as well as some choice covers. (“All Van Halen songs,” Claypool quips.) The bassist promises that they will adhere to current live music rules and offer “a strong setlist to draw from so we can mix it up every night.” He even hopes to dust the cobwebs off of some selections that have fallen out of his repertoire in recent years.

Just a few days into their first full run, Claypool will also make his eighth stop at Bonnaroo—and first since 2011—as part of the festival’s 15th-year celebration. He has a long history with Superfly, the festival’s promoters. Claypool was one of the first acts to play Bonnaroo’s main stage in 2002 and famously formed Oysterhead for their signature SuperJam during the New Orleans Jazz & Heritage Festival in 2000, laying the groundwork for the future festival.

His role as an alt-rock ambassador to jam-nation helped set the tone for Bonnaroo’s eclectic nature. “I see the jam scene as floating in and out of me,” he says of his recent work, which has shied away from some of the dark, all-out improv of his Frog Brigade and the looser version of Primus he fronted after the band reunited a few years ago. “Primus has been tighter with less of the improv stuff now that Herb [drummer Tim Alexander, who rejoined the band in 2013] is back and we’ve been touring with Tool. It’s not that Herb says, ‘I don’t want to play improvisationally based music,’ but that was [previous drummer] Jay Lane’s world, going all over the place. We definitely still have our space sections within certain songs, whether it’s ‘Pachyderm’ or ‘American Life,’ where you just take it to the moon.”

Looking back on his initial foray into the jamband scene with Oysterhead, Claypool says that Anastasio agreed to join the group only if Copeland was involved because he probably “didn’t really want to do it” and figured The Police drummer would never sign on. Little did Claypool know that the one-off gig would introduce him to a new, open-eared audience and give him the courage to venture into the ether with Primus and his various other projects. “That really opened my eyes to the notion: ‘Hey, there are people out there that want to see you dance on the edge and just see if you can fall off or not, or just see how gracefully you do fall off,”’ he says.

While it remains to be seen just how jam-heavy the Delirium’s shows will feel, Lennon notes that he’s dipped his toes into free-form waters with Mystical Weapons, his all-improv project with Deerhoof’s Greg Saunier. “The fact that I’m going to be improvising with Les…,” Lennon says before trailing off. “All I can say is: ‘I’m practicing.’”

“Sean’s a freak—he can go out there,” Claypool says. “We were all pleasantly surprised when he sat in on ‘Pachyderm’ that night. A big part of the jam element is the lack of fear, and he was fearless out there. He’s got a great sensibility, and he grabbed the ball and ran with it. I plan on tossing him the ball quite a bit. He’s not afraid to jump in and swim.”