In the past year, Elizabeth Holmes, founder and CEO of Theranos, has proven impressively tenacious. She stood firm as her once promising biotech company faced scandal after scandal—from the revelation that its “revolutionary” blood testing technology doesn’t work and her lab endangered patients’ health, to the federal sanctions that shut down the company’s labs and banned Holmes from the business altogether. Equally tenacious, it seemed, were Theranos’ investors. Amid the blows, they stood quietly by or professed their faith in Holmes and her embattled company.

All that has changed. According to the Wall Street Journal, one of Theranos’ largest investors, a California-based hedge fund named Partner Fund Management LP, filed a lawsuit against the company Monday afternoon. The suit, filed in Delaware under seal, alleges that Theranos deceived PFM in order to net a nearly $100 million investment from the hedge fund in 2014.

In a letter to its own investors that was reviewed by the WSJ, the hedge fund wrote:

Through a series of lies, material misstatements, and omissions, the defendants engaged in securities fraud and other violations by fraudulently inducing PFM to invest and maintain its investment in the company.

The letter goes on the explain that Holmes and her colleagues assured PFM that Theranos’ blood testing technology worked and was close to getting approvals from federal regulators. PFM, a 12-year-old fund that manages $4 billion, said it has never before been involved in a lawsuit and only filed in order to protect its investors.

In a statement on its website, Theranos fired back: “The suit is without merit, the assertions are baseless, and the plaintiff is engaging in revisionist history.”

Whether Theranos committed fraud is up to the courts to determine, but it’s clear that PFM’s complaints about the shortcomings of the company’s technology are accurate. Media reports and federal inspections that started coming out late last year revealed that Theranos had stopped using its own technology due to accuracy issues and only received FDA approval for one of more than 200 tests it advertised. In May of this year, the company ended up correcting or voiding tens of thousands of old blood test results in an attempt to mollify federal regulators.

The move wasn’t enough, however; Theranos is still reeling from the hefty sanctions levied against it by the Centers for Medicare and Medicaid in July. The company is currently seeking an appeal but seems to expect to fail. Last week, Holmes announced that Theranos is shutting down all of its labs and will put all of its efforts into manufacturing commercial blood testing devices.

In an open letter to investors announcing the company’s pivot, Holmes’ noted: “We are fortunate to have supporters and investors who believe deeply in our mission of affordable, less invasive lab testing, and to have the runway to realize our vision.”

However, Theranos’s new technology, the miniLab, has much more modest goals than the company’s earlier devices. The miniLab basically aims to miniaturize and combine standard lab testing methods into one portable device—convenient but not revolutionary. Whereas Theranos made its name and attracted investors by claiming that its technology could perform dozens of tests with just a drop of blood from a finger prick. The claim attracted around $800 million in investments, including $96.1 million from PFM. Around the same time, Theranos earned a valuation as high as $9 billion from investors, which has since dropped to just $800 million.

In addition to PFM’s lawsuit, Theranos is under investigation by the Securities and Exchange Commission. The WSJ also points out that another big investor, Lucas Venture Group, scrubbed from its website all references to its investment in Theranos.