If you’ve ever tried to get ice cream at a McDonald’s restaurant, there’s a better-than-average chance you were stymied in your quest for soft-serve goodness by an out-of-order ice cream machine. A new report from Wired attempts to get to the bottom of the mystery of the McDonald’s ice cream machines, why they have a secret repair menu that most McDonald’s workers don’t have access to, and one couple’s attempts to hack the machines for the greater good.

…after years of studying this complex machine and its many ways of failing, O’Sullivan remains most outraged at this notion: That the food-equipment giant Taylor sells the McFlurry-squirting devices to McDonald’s restaurant owners for about $18,000 each, and yet it keeps the machines’ inner workings secret from them. What’s more, Taylor maintains a network of approved distributors that charge franchisees thousands of dollars a year for pricey maintenance contracts, with technicians on call to come and tap that secret passcode into the devices sitting on their counters.

It’s weird to consider that a company the size of McDonald’s would be hampered by what is mainly a right-to-repair issue. The restaurants have to use Taylor’s repair techs, and the machines themselves tend to be fragile and temperamental, according to franchisees bound to use the machines by agreements with McDonald’s. So Jeremy O’Sullivan and Melissa Nelson created a device that would hack into the machines and provide diagnostic info, including access to the secret menu. They called it Kytch.

One franchisee, who asked that WIRED not identify him for fear of retribution from McDonald’s, told me that the ice cream machine at one of his restaurants had been down practically every week due to a mysterious failure during its pasteurization cycle. He’d scrutinized the assembly of the machine again and again, to no avail.

Installing Kytch revealed almost instantly that an overeager employee was putting too much mix in one of the machine’s hoppers. Today he wakes up every morning at 5:30, picks up his phone, and confirms that all his machines have passed their treacherous heat treatment. Another franchisee’s technician told me that, despite Kytch nearly doubling its prices over the past two years and adding a $250 activation fee, it still saves their owner “easily thousands of dollars a month.”

I’m not going to spoil the plot twists, but suffice to say that Wired reporter Andy Greenberg tells the tale of the ice cream machines and the well-intentioned hackers almost like a spy thriller; I was half-expecting a Jason Bourne-like hero to come in and set everything right. Go read this fascinating deep dive into the wonky ice cream machines that even McDonald’s itself jokes about.