At about 1100 central time, a Mooney M20M suffered an in-flight fire shortly after takeoff from the Destin-Ft Walton Beach Airport. The pilot was able to return for landing but suffered serious burn injuries. The pilot said he departed from runway 32 and was climbing through about 2,500 to 2,800 feet when the cockpit was enveloped in thick black smoke and flames appeared underneath the instrument panel behind the rudder pedals on both sides of the cockpit. He turned off the master switch and initiated a descending left turn with the intention of ditching the airplane. He reduced the mixture control and opened the cabin entry door in anticipation of ditching but he was able to see outside and elected to return to the airport for landing. Post-accident investigation revealed the nut holding the clamp used to secure the turbocharger exhaust pipe was missing, allowing the turbocharger to spew hot gas into the engine compartment.