AT 2135 EST, THE PLT CALLED THE LANSING FSS & REQUESTED A WX FORCAST FOR THE DETROIT CITY ARPT & WINDS ALOFT. HE WAS BRIEFED, BUT HE DID NOT FILE A FLT PLAN, SOMETIME AFTER 2200 EST, HE TOOK OFF FORM MASON, MI ON A PASSENGER FLT TO ANN ARBOR, MI. AT 2252, THE PLT CALLED THE LANSING FSS & OBTAINED THE CURRENT LANSING WX. AFTER LANDING AT ANN ARBOR, TWO ADDITIONAL NIGHT, PASSENGER FLTS WERE MADE (TO THE DETROIT CITY ARPT & BACK TO ANN ARBOR). AFTER THE 2ND LANDING AT ANNN ARBOR (APRX 0200), THE PLT WENT TO A RESTAURANT 'FOR SOMETHING TO EAT.' AT APRX 0400, HE TOOK OFF ALONE ON A FLT BACK TO MASON. AT ABOUT 0426, THE ACFT CRASHED APRX 11.5 MI NW OF THE DEPARTURE ARPT. THE ACFT IMPACTED ON A WESTERLY HEADING IN AN ESTIMATED 58 DEG DESCENT. A WITNESS ABOUT 3/4 MI NNW OF THE CRASH SITE SAID THE ACFT SOUNDED LIKE IT WAS ON A SE HEADING WHEN IT PASSED OVER HER HOME. AN EXAM OF THE WRECKAGE REVEALED NO EVIDENCE OF A PREIMPACT MALFUNCTION OR FAILURE. UNFAV WX, LOW CEILING, RAIN & FOG WAS FORMING. AT 0530, HVY FOG AT DEXTER. NO CURRENT MED CERT.