Investors got back into the buying spirit on Friday, sending nine out of 10 sectors higher, as all three major U.S. indices gained ground today. On Wednesday, the World Bank revised the estimate for global growth in 2014 lower, to 2.8% from 3.2%, and yesterday's sectarian violence in Iraq sent stocks plunging, yet again. But on Friday, those fears were largely dismissed or ignored by Wall Street, and the S&P 500 Index (^GSPC -0.22%) added six points, or 0.3%, to end at 1,936. The Priceline Group (BKNG -0.40%), Edwards Lifesciences Corp. (EW -0.91%), and Citigroup, (C 0.26%), however, each finished the day in the red, ending as some of the worst stocks in the benchmark index.

The Priceline Group was Friday's single largest laggard in the S&P 500, tumbling 3%. Priceline didn't make a costly PR gaffe, or receive any damning analyst downgrades; Wall Street punished the stock merely because it acquired restaurant-booking website OpenTable for $2.6 billion. In fairness, Priceline did pay a hefty premium for its stake -- a 46% premium to Thursday's closing price, as a matter of fact -- but in return, Priceline diversifies its business and gets a company that's nearly tripled its annual sales since 2009.

The only sector of the markets that didn't gain ground today was the health-care sector, where medical appliances manufacturer Edwards Lifesciences makes its bread and butter. The stock shed 1.9% on Friday, as investors continued to punish the company for saying that its growth will likely be affected by competition this year. The silver lining is that the company, which specializes in making devices that treat heart ailments and disease, sees industry-beating growth beginning in 2015. Edwards Lifesciences also just received a $1.1 billion patent infringement settlement from rival Medtronic last month, so investors can be thankful for a big payout and, of course, fewer legal fees in the future.

Source: Public domain

Finally, shares of Citigroup lost 1.4% today after reports that the Justice Department is preparing to sue the company for its role in selling mortgage-backed securities that went sour, causing a ripple effect that helped to create the financial crisis. In what must be one of the most dysfunctional love/hate, public sector/private sector relationships in history, Citigroup received $476 billion in cash and guarantees during the financial crisis to keep it afloat. Today's reports allege that the bank refused to pay more than $4 billion to the Justice Department during negotiations for its role in the economic collapse.