Conspiracy nuts can rest easy today. Cynics can take a chill pill. Twenty-four hours after Jackson Hewitt Tax Service (NYSE: JTX) leapt 17% in one day's trading, apparently on no news whatsoever, the mystery is revealed.

I imagine that, like many of my fellow investors, I was checking my portfolio online yesterday, and was ... well, "shocked" is too weak a word to describe my reaction when I saw that my stock in Jackson Hewitt had increased that much in value. "Great news must be afoot," I thought. And I then proceeded to look for the announcement that H&R Block (NYSE: HRB) or Intuit (Nasdaq: INTU) had bid to acquire the troubled Motley Fool Inside Value recommendation.

A fruitless endeavor
Alas, my search was in vain. There was no news of a buyout. Or of going-private. Nor, for that matter, had Action Jackson announced that, oops, it misplaced a decimal and would now restate its financials to show that last quarter wasn't nearly as awful as it had initially reported.

In short, there was no news whatsoever to explain the skyrocketing shares.

Until ...
This morning, pointed out that Goldman Sachs (NYSE: GS) has advised its clients to buy Jackson Hewitt, calling the valuation "attractive." While its description of the action was not entirely accurate ( deemed it a Friday upgrade) the website's info set me on the right track. I've since discovered that the upgrade in question actually came out yesterday, in the middle of the trading day.

So this explains the inexplicable rise in the price of shares that had -- before yesterday -- lost nearly two-thirds of their value over the past year. But does it justify the new price? Sad to say for a shareholder like me, but no, I do not believe it does. Obviously, investors (at least, those lucky enough to have noticed Goldman's upgrade yesterday) place a lot of faith in the investing superstar's "buy" thesis. But when I look at what I now own, I see a stock selling for 11 times trailing earnings, which most analysts agree will not grow faster than 10% per year over the next half decade.

Moreover, the stock is currently generating just two-thirds as much free cash flow as it reports in net income -- the first time in six years that it's been "upside down" in this cash profits/accounting profits equation. Maybe Goldman's right on this one. Maybe Jackson Hewitt can turn itself around and return to its winning ways. But for now, for me, the numbers just don't add up to "buy."

Do the bargain-hunting Fools at Motley Fool Inside Value agree with me? More often than not, they don't. But to find out for sure, all you need to do is claim your free, 30-day trial to the service right here. Jackson Hewitt is a recommendation of Inside Value and of Motley Fool Hidden Gems Pay Dirt.

Fool contributor Rich Smith does not own shares of any company named above. The Motley Fool has a disclosure policy.