Valeant Pharmaceuticals was having a good year. After the failed attempt at a hostile takeover of Allergan in 2014, a smaller acquisition this year, Salix Pharmaceuticals, went relatively smoothly. In the summer (August 5th to be precise) the company’s share price experienced a record high of 262.52, over 80% higher than the 144.45 level it was on at the start of the year.

Yet at the time of writing (18:11 BST on Thursday 22nd October), Valeant Pharmaceuticals is trading at 97.89, a drop of staggering proportions (Valeant stock later closed at 110.21, which was still a 7.08% drop on the previous day). What happened?

Arguably the bad news started for Valeant just over a month ago, when a range of pharmaceutical companies took a hit in the wake of a tweet by Hillary Clinton. The presumptive Democratic nominee criticised ‘price gouging...in the specialty drug market’ and announcing her intention to combat it.

However, the September drop was due to generalised criticism, with no mention of Valeant. Earlier this week, that changed. On Monday the New York Times ran a story entitled ‘Drug Makers Sidestep Barriers on Pricing’, in which Valeant was directly named as one of a number of pharmaceutical companies using so-called ‘specialty pharmacies’. Such pharmacies make it easier for doctors to prescribe the drug in question; they also enable the pharmaceutical companies to charge inflated prices for some of their products. The article also mentioned a specialty pharmacy affiliated with Valeant, Philidor Rx Services.

The timing of the article was unfortunate for Valeant, given that Federal Investigators served Valeant with a subpoena last week related to the way it prices and distributes its products. Furthermore, there was another interested party which lost no time in attacking with force.

Citron Research describes itself as a ‘stock commentary website’ which ‘has amassed a track record identifying fraud and terminal business models’.  In late September it released a report aimed squarely at Valeant, something which they made perfectly clear from the start with lines such as ‘This is not a biotech problem, it is a Valeant problem’ and ‘The Real Problem with drug pricing in America is forged in a single word: Valeant.’ The report described Valeant’s practice of hiking prices on its products – the biggest increase being a 2288% increase in the price of eardrops over a 2 and a half year period, but many other drugs seeing price increases of hundreds of percent – and the company’s tax inversion.

The response from investors to the report was relatively limited. However, Citron made it clear that this was only the first part of its research piece on Valeant and that more was to come. The second half of that report was published in the wake of the New York Times Piece and contained a title guaranteed to get any investor to sit up and take notice;

‘Valeant: Could this be the Pharmaceutical Enron?’

In the document, Citron accused Valeant of creating ‘an entire network of phantom captive pharmacies... merely for the purpose of phantom sales or [to] stuff the channel, and avoid scrutiny from the auditors.’ It also accused Valeant of playing a part in a sham transaction worth $69 million related to one of these ‘phantom pharmacies’.

Citron released the report on Wednesday morning; when the markets opened, Valeant stock plummeted by close to 40%. It didn’t take long for Valeant to respond; just a few hours later the company put out a press release responding to Citron’s allegations, calling them ‘erroneous’. This, plus a public statement of confidence from major shareholder Bill Ackman (who backed up his words with capital by buying another 2 million Valeant shares), helped Valeant recover some of the ground it had lost, though the stock still closed down by close to 20%. However, the next day saw the stock drop again, with investors clearly not pacified by Valeant’s response.

So, what now? Well, it remains to be seen whether Valeant will be able to properly answer all of the questions raised by Citron. However, another element to consider, as Fortune pointed out, is that Valeant has a giant debt-load, brought about by years of takeovers; its debt-to-equity ratio is huge compared to many of its competitors.

One thing is for sure; this story is far from over.