Led Zeppelin appeared to lead something of a charmed existence during the early part of their career, enjoying blockbuster success with fans in spite of negative reviews from critics and quickly earning a spot near the top of the rock 'n' roll pantheon. But by the mid-'70s, they seemed to be suffering from a curse, as multiple setbacks kept them from capitalizing on the momentum they'd built – and on July 26, 1977, when singer Robert Plant suddenly lost his five-year-old son Karac to a stomach virus, it nearly split the band completely.

The Plant family's terrible tragedy came during what was supposed to be a triumphant American tour for Zeppelin. Two years earlier, the band had been forced off the road for an extended spell when Plant and his wife were involved in a serious car accident while visiting the Greek island of Rhodes. But even if the time off helped Plant recuperate from his injuries, it did nothing to prevent a series of disasters that dogged the tour, starting with Plant picking up a case of laryngitis that forced the group to push its first date back from February to April.

Ticket sales were still strong, but the postponement had a ripple effect. As guitarist Jimmy Page later pointed out, the band's equipment had already been shipped overseas, complicating any efforts to rehearse. "We didn't have any instruments for a month," he once lamented. "All the equipment was shipped over there five days before we were due to go. I didn't play a guitar for a month. I was terrified at the prospect of the first few shows."

Once they were finally able to get out in front of fans, the problems continued to pile up. An April 1977 stop in Cincinnati was marred by violence when a group of ticketless fans tried to force their way into Riverfront Coliseum, and a "mini-riot" broke out after their June concert in Tampa ended up being rained out partway through the set. Things got even uglier the following month, when manager Peter Grant led a group – including drummer John Bonham – into the savage beating of a Bill Graham employee following their July 23 performance in Oakland, Calif.

"There was an extraordinary amount of tension at the start of that tour," a band employee later recalled. "It just got off to a negative start. It was definitely much darker than any Zeppelin tour ever before that time ... The kind of people they had around them had deepened into some really criminal types. ... They still had their moments of greatness (but) some of the shows were grinding and not very inspired."

Listen to Led Zeppelin's 1977 Performance at Tampa

After making their way out of Oakland, the band members made their separate ways to the next stop on the itinerary, a planned appearance in New Orleans. Shortly after arriving in the city, Plant received the devastating news, half a world away and helpless to join his son during his confusing final moments. "The first phone call said his son was sick," said tour manager Richard Cole, describing a fateful pair of calls from Plant's wife. "And the second phone call, unfortunately, Karac had died in that time."

"Karac was the apple of Robert's eye; they idolized one another," said Plant's father in an Associated Press report announcing the immediate cancellation of the tour, which had been scheduled to run into August. Searching for answers about the sudden illness, Plant retreated home, taking comfort from his wife Maureen and daughter Carmen while Zeppelin went on hold. As Page later put it, "We were all mates. We had to give the man some space."

That didn't mean Plant shut out his bandmates, however. "After the death of my son Karac in 1977, I received a lot of support from [Bonham], and I went through the mill because the media turned on the whole thing and made it even worse," Plant told Barney Hoskyns. "I had to look after my family and at that time, as we regrouped, I applied to take a job at a Rudolph Steiner training college in Sussex. I wanted to just get out of it – to go away and forget it."

In a separate talk with Rolling Stone, Plant said "I lost my boy. I didn't want to be in Led Zeppelin. I wanted to be with my family." He also later claimed to have quit all of his chemical habits cold turkey. "I stopped taking everything on the same day," Plant added. "The most important thing to me is my family and when I got off my face, I found it difficult to be all things to the people that meant a lot to me."

Plant was quite serious, at least for a time, about pursuing a new career in education, too. Admitting that "it's not something that we, as a family, have been able to get over yet," he told GQ in 2011 that "our family had always been close to the Rudolf Steiner Waldorf education in the West Midlands and I just liked the way it all worked. ... I just thought there was something far more honest and wholesome about just digging in and putting the ego away in the closet. Because no matter what we say, entertainers are usually quite insecure, wobbly characters underneath – and maybe that bit of glory or that bit of expression or whatever it is compensates in some area. But I thought I should be rid of it. Yeah, I thought it was not a bad idea. Sometimes, I still feel like that."

Listen to Robert Plant's Tribute to Karac, 'All of My Love'

In 2013, Plant remembered that "during the absolute darkest times of my life when I lost my boy and my family was in disarray, it was Bonzo who came to me. The other guys were [from] the South [of England] and didn’t have the same type of social etiquette that we have up here in the North that could actually bridge that uncomfortable chasm with all the sensitivities required ... to console."

Zeppelin biographer Mick Wall took Plant's comments a step further, claiming that the distance Robert Plant describes was even more profound -- and that when Jimmy Page, bassist John Paul Jones, and Grant declined to appear at Karac's funeral, it created a rift that never truly healed. "Until then, Robert was still in thrall to Jimmy and what he had created with Zeppelin. After that incident, Jimmy no longer held the same mystique for Robert," Wall claimed in 2011. "It was also the beginning of Robert having much more power over what the band did or didn’t do next. He truly no longer cared and therefore was ready to walk at any point if they didn’t fit in with him. And that’s the way it remains to this day."

But if Bonham stayed closest to Plant's side during the months following Karac's death, it was ultimately Page who talked him out of retiring from music. "I was thinking about leaving the group, but Jimmy Page kept me from doing it," Plant said in an interview at the time. "He said without me, the band's nothing. He wanted me to take a break until I felt ready for playing again. I realized that we are more than business partners. We are real friends. We have enough money to live a life without troubles, but nobody knows how long our fans can wait. They might forget us if we don't play anymore. I don't want this to happen to the band. Our friends kept calling us every day. They helped us through this."

To Zeppelin fans' everlasting regret, the road ahead for Zeppelin wouldn't last much longer; although they soldiered ahead for 1979's In Through the Out Door, Bonham's sudden death on Sept. 25, 1980 ended the band as a creative unit once and for all. And although it's impossible to know what they might have accomplished together if he hadn't passed away, the group's final days found them in an artistic flux, struggling to move forward while coming to grips with what they'd been through.

"In Through the Out Door wasn't the greatest thing in the world, but at least we kept trying to vary what we were doing, for our own integrity's sake. Of all the records, it's interesting but a bit sanitized because we hadn't been in the clamor and chaos for a long time," Plant pointed out in 1990. "In '77, when I lost my boy, I didn't really want to go swinging around. 'Hey hey mama, say the way you move' didn't really have a great deal of import anymore."

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