The precocious CEO of consulting firm Accordion Partners is the first call of private equity executives when they need help quick.

Nick Leopard, 32, on the roof of Accordion's office in downtown Manhattan

FORTUNE -- Pam Hendrickson needed reinforcements. Recently the chief operating officer of the Riverside Co., a private equity firm that owns more than 80 companies on four continents with combined sales of $3.2 billion, was trying to deliver a five-year budget for all of Riverside's operations. She found herself shorthanded -- one key employee was on maternity leave, another had just left -- and the task required masterful financial modeling skills. In a bind, she turned to Nick Leopard. Says Hendrickson: "Anytime we need analytic help, Nick is my first call."

Leopard, 32, is the CEO of Accordion Partners, a financial services consulting firm that he founded in late 2009. Leopard and his team of 25 bankers act as a sort of rapid-response unit that can drop into a private equity firm or one of its portfolio companies and fix problems of all kinds -- temporarily expanding management's capacity, as the name Accordion suggests. "As much as private equity firms push, the management teams at their portfolio companies often can't build extremely complex forecasts," says Leopard. "So then there are surprises that no one saw coming." Leopard specializes in minimizing those unwanted surprises.

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A former lacrosse goalie at Saint Joseph's University, Leopard began his career at the commercial lender CapitalSource (CSE) in 2002 before moving to investment banking at Bear Stearns in 2005. In 2007 he joined the investment team at BHC Interim Funding, a $200 million mezzanine debt fund. Along the way he formed a network of future clients like Providence Equity Partners and Riverside.

As the financial crisis unfolded in 2008, Leopard concluded that Wall Street was going to change: Headcounts would shrink, dealmaking would slow, and buyout firms would have to hold on to portfolio companies longer. He sensed an opportunity. "You could see that the buyout firms were going to get strapped but would still want to give their portfolio companies extra help when the economy slowed," he says. Leopard has purposely kept Accordion's business model flexible. For example, his team can advise on M&A transactions like an investment bank. But unlike a bank, which makes fees on completed deals, Accordion bills strictly for its bankers' time. The firm is paid even if the deal doesn't get done, so there's no built-in incentive to push for a bad transaction.

In September, Accordion launched a new practice called CFO Leadership Services. The idea is to help companies manage investor relations, risk management, compliance, and crisis situations. Leopard says he sees another void in the market in those areas. And he's ready to fill it.

This story is from the November 12, 2012 issue of Fortune.