A cassette case scattered into the Dakota archway as murderer Mark David Chapman stood over John Lennon. Inside was the completed mix of Yoko Ono's "Walking on Thin Ice" with one final mind-bending solo from the former Beatles star, played on an historic guitar.

The Jack Douglas-produced "Walking on Thin Ice" found Ono again in a rangy mindset, pushing Lennon to the edges of his muse. Lennon had assumed a sideman's role with Ono before, notably on early '70s albums like Fly and the then-just released Double Fantasy, but this track would be different.

Dominated by edgy dance beats and patently weird Ono vocal, "Walking on Thin Ice" is the sound of Lennon leaving behind convention. It was nothing like the gossamer, deeply content music from the studio project they'd recently issued together. This was a classic rocker unshackled.

"Walking on Thin Ice" had originally been pieced together through seven takes, during sessions begun in August 1980 at the Hit Factory. This early version found a home in an initial running order for Double Fantasy from later the same month, but was ultimately set aside in favor of Ono's "Kiss Kiss Kiss."

"I wanted to push it a little further, experimentally," Ono told Madeline Bocaro in 2016.

Work on Double Fantasy concluded in mid-October 1980, and the album followed that November. Lennon was reportedly all set for a short vacation before firming up plans for a tour. But then he called Douglas, intent on returning to Ono's "Walking on Thin Ice."

"We're going back again," Douglas later remembered Lennon telling him. "I feel like I just don't want to leave the studio. Just you and me and Yoko, that's all I want."

Douglas created a loop from the earlier takes for Ono and Lennon to build upon. She recut her vocal, but felt something was still missing. Then Ono hit upon the idea of a closing spoken-word segment.

"That feeling came to me after we recorded it, but I wasn't sure about it," she told American Songwriter in 1992. "I just knew it had something to do with a girl who is walking. Then I sang the song, and I was still sitting in the chair by the mic, waiting for them to change the tape. That's when it just came. So, I just wrote it down quickly. I said, 'I got it!'"

The image in her mind traced back to a recent trip to Chicago. "Lake Michigan is so big that you don't know the end of it when you look at it," Ono added. "I was visualizing Lake Michigan. I was just thinking of this woman that is walking Lake Michigan when it is totally frozen, and is walking and walking – but not knowing that it's that huge."

Listen to Yoko Ono and John Lennon Perform 'Walking on Thin Ice'

Lennon was intently listening, taking it all in. Douglas said "John knew that Yoko was onto something with that one – especially with that spoken word. And the whole feel of it was so different that she was going to have a hit."

Ono discussed what direction Lennon's guitar part might take, but only in the most general of ways. "We'd talk about it – like, I would say, 'I'm going to go like this; you go like this,'" Ono told American Songwriter. "I don't mean 'go like this' in terms of notes, but just the mood of it."

Back in the studio on Thursday, Dec. 4, Lennon was moved to pull out his black 1958 Rickenbacker 325, a guitar he debuted for American audiences during the Beatles' 1964 appearance on The Ed Sullivan Show. He apparently hadn't used it since a George Martin-led session in the mid-'60s.

Douglas worked the Bigsby whammy bar while Lennon played, creating an eerie vibrato that shrouded everything in a dark new ambience. A mixture of very old with strikingly new, Lennon's contribution finally completed "Walking on Thin Ice."

Critic Robert Palmer hailed Lennon's "crashing, distorted guitar solo," describing it as "brilliant, pulse-quickening rock 'n' roll brinksmanship" in a 1981 review for the New York Times. "Nobody can play like that," Ono says in Ken Sharp's Starting Over: The Making of John Lennon and Yoko Ono's 'Double Fantasy.' "John was always saying, 'Nobody notices my guitar playing,' but he just blossomed. The avant-garde thing that I did, that's where he could do that kind of wild guitar playing."

Lennon ended up spending the following weekend lost in thought, playing the almost-completed version of "Walking on Thin Ice" over and over on Saturday and then into the night.

"It was unlike him that he took so much time on it," Ono told Rolling Stone in 2010. "I went to sleep. When I woke up on Sunday morning, he was still playing 'Walk­ing on Thin Ice,' as he looked over the park. I knew the song was a good song, but I was just thinking of what else should be done musically. Never thought deeper than that at the time. Only just recently, it occurred to me that maybe John was aware of the song in a different light."

Listen to the Pet Shop Boys' Hit Remix of 'Walking on Thin Ice'

Monday, Lennon's last, would be a busy day. They had a photo session with Annie Leibovitz and an appearance on a radio program scheduled, then final mixing and mastering for "Walking on Thin Ice" was to begin at 6PM. Listening to the playback, Lennon was overcome with anticipation: "From now on, we're just gonna do this. It's great!" he enthused. "This is the direction!"

They worked late into the evening of Dec. 8, as Lennon continued celebrating the discovery of this thoroughly modern new musical thread. "I think you just cut your first No. 1, Yoko," he added, in studio chatter that she later appended to the song for 1992's Onobox retrospective set. Then, Lennon and Ono headed back home to the Dakota.

"I said, 'Goodnight, see you in the morning' at Sterling, the mastering studio – and a few minutes later I get a phone call, he's been shot," Douglas told the Gothamist in 2016. "I couldn't believe it. I went up to Roosevelt Hospital, spent the night there, but he was already gone. They didn't announce it until 6 in the morning."

Lennon's next phase never happened. In a sad and terrifying twist of fate, Ono was instead living the lyrics to their final musical statement together.

"There's some songs that start to affect our life," Ono told Seconds magazine in 2005. "I found that it's true with many of my works. After I wrote 'Walking on Thin Ice,' my life was literally like walking on thin ice."

The single didn't arrive until Feb. 6, 1981, after a protracted period of mourning. Ono paired "Walking on Thin Ice" with "It Happened," a now-poignant song about isolation originally composed during her '70s-era estrangement from Lennon.

"At the time, it had to do with moving away from each other but then, when John died, I thought, 'Oh, that's what it was about,'" Ono told American Songwriter, with a rueful laugh. "I look at that period [popularly known as Lennon's "Lost Weekend"] like a rehearsal ... for the big separation that I didn't know would happen. It was very good that I had that rehearsal in terms of moving along. That helped me later."

"Walking on Thin Ice" initially stalled at No. 58 on the Billboard Hot 100, before fading. It looked like Lennon's prediction wouldn't come true.

Then, decades later, the song found new life at discotheques – finally hitting No. 1 on the dance and club play chart in 2003. At 70, Ono became the oldest person to accomplish that feat. "Walking on Thin Ice" returned to No. 1 in 2013, making Ono just the third act (after Jennifer Holliday and Jody Watley) to take the same track to the summit of that chart twice.

"John immediately thought it would be my first No. 1," Ono mused in a 2013 interview with Songfacts. "Well, it didn't happen right away – but he was right."

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