Even as she watched actors take their bows for History Theatre’s “Glensheen” in 2015, Tami Foster knew she wanted more. Luckily, the musical returned the next year, so she was able to see it again. And again. And again. Four times.

So far.

With songs by Chan Poling and a book by Jeffrey Hatcher, the dark comedy inspired by the notorious 1977 murders at the titular Duluth mansion was such a hit when it debuted in October 2015 that it returned the next summer. Since then, it has become an annual, “Christmas Carol”-like cash cow for History Theatre, racking up ticket sales and newcomers (after its first run, subscribers rose from 1,700 to 2,500). Its record-breaking fifth run starts Saturday, with all but one of the original actors (Adam Qualls) returning. Only a fool would bet it won’t be back for a record-breaking sixth.

“It sounds weird to say that it’s a play about these murders that happened in real life but it’s funny and it’s a musical. How can that be?” said Foster. “But they do it in a way that isn’t disrespectful” to Duluth’s Congdon family, whose matriarch, Elisabeth, was a victim along with her nurse. Foster has seen “Glensheen” each year and will bring a group of 10 to this summer’s revival. Most have never been to History Theatre.

That is macabre music to the ears of artistic director Ron Peluso, who had no idea he was looking at History Theatre’s biggest hit when it opened four Octobers ago. At least not until the second week of “Glensheen’s” initial run, when it occurred to him they should stow the set in the basement for a possible return. By then, it was hard to remember that the murderous material once made him so nervous that he didn’t agree to commission the musical until actor/director Austene Van called him a “chicken” for shying away from it.

“It felt like risky business, doing a musical about the murder of two elderly women. But Jeff and Chan wrote a really smart, wickedly funny and yet respectful show,” said Peluso, whose theater didn’t program plays in the summer until it realized “Glensheen” could fit there as a bonus, non-subscription offering. “We didn’t think last summer would be as successful as the summer before but it exceeded expectations, so we thought, ‘I guess we should do it one more time.’ Right now, it’s living up to last year’s timeline, so the question is: Should we do it again?”

Foster’s answer is an emphatic yes. She’s a Repeat Offender, the name given folks who return to the show every season. The Burnsville hairstylist, who first visited Duluth’s Glensheen Historic Estate on a sixth-grade field trip in 1980, may be the play’s ideal audience.

To wit: She has returned to the mansion seven times and is planning an eighth to see a display of Congdon gowns. She’s a fan of the Suburbs, the local band Poling leads. And Foster, 50, has been compelled by the murders as far back as that class trip.

‘Is this where they killed those ladies?’

“I remember already knowing about the murders, but they told us, ‘Do not ask about the murders. You’re not allowed.’ At that point, the tours didn’t talk about them at all. But, of course, within five minutes of walking in the door, some class clown was like, ‘Is this where they killed those ladies?’” recalled Foster.

“The house is amazing and it’s right there on [Lake Superior] and you can see the Lift Bridge when you look around. It’s all so pretty, and the story behind the murders and the family is so intriguing.”

Foster briefed her group but some of them aren’t familiar with the Glensheen legend, so she’s curious whether they’ll enjoy the musical as much as she does.

Familiarity has been a sticking point in attempts to get the smash produced elsewhere. History Theatre is raising funds to tour to three cities in Minnesota and has lined up a representative to market “Glensheen” around the country. But, so far? Crickets.

“We did a little workshop production for Ken Davenport, our New York producer friend, of it and [the Bobby Vee musical] ‘Teen Idol,’ and I remember him saying, ‘It’s nice you have this cute little play about Minnesota but, you know, all the plays in New York take place in New York.’ And I said, ‘Um, you mean like “Phantom of the Opera” [Paris] and “Fiddler on the Roof” [Russia]?” Peluso recalled.

One Repeat Offender who advised the History Theatre that “Glensheen” would sell tickets outside Minnesota is Jane Davies. A pal of “Glensheen” actor Dane Stauffer, the Pittsburgh resident has seen the show 16 times, with a 17th and 18th already booked. The first time she saw it, Davies knew almost nothing about the murders.

“It’s so cleverly done that you don’t need to know. And they give you the background in the program,” said Davies.

Like Foster, Davies’ favorite aspect of the musical is Wendy Lehr, although they differ on which of Lehr’s several roles is best. Foster loves Lehr’s performance as the attorney of accused conspirator Marjorie Caldwell, called Ron Beshmesher in the show. But Foster opts for the song, “Stay With Me,” with Lehr as Congdon’s nurse, Velma, overruling her husband as he urges her not to go to Glensheen on what would turn out to be the last night of her life.

“It brings tears to my eyes. It gets me every time,” said Davies.

“Glensheen” has fresh stuff this year for longtime fans. The new cast album is for sale and the 2 p.m. Aug. 3 performance will be an experiment: On select numbers (not the sad or painful ones), the audience will be encouraged to sing along.

Peluso plans to pass out lyric sheets to theatergoers but, if Foster and Davies are any guide, some will already know the words by heart.