Activism giveth, and wild market turmoil taketh away.

Harbinger Capital Partners, which was up almost 43% at the end of the first half, has given back all of its gains and more. The firm’s $14 billion flagship fell another 17.9% last month—one of the worst months in the history of the hedge fund industry—and is now down 5.4% on the year.

And the bad news may not be over for the $21 billion firm: Investors say there will be further losses from Harbinger’s exposure to Lehman Brothers, which has already cost it $600 million, the Financial Times reports.

But Harbinger chief Phillip Falcone, who made his name with a big, successful subprime mortgage bet last year and with his successful battle for board representation at The New York Times Co., has more than just Wall Street’s woes to blame for his fund’s poor performance. The firm recently lost its activist battle with mining concern Cleveland-Cliffs, where it had sought changes to its shareholder rules.

Meanwhile, Harbinger says it is taking steps to foster a turnaround, including a reduction in the amount of leverage it uses.