E320 W124 big puff smoke, now won't start

[tan man]

Unfortunately, I can only relay the symtoms as my wife recalls them because it happened when I wasn't there. She says she tried to start the car, there was a big cloud of smoke from under the car so she shut it down. Now the car won't start.
Best I can make out from her description the smoke was coming out from underneath the car, it was visible to her so it must have been from the front or mid and not rear of the car.
I didn't see any fluid leaks on the ground. Tried to start it myself, car cranks but won't turn over. It happened tonight so on Saturday when I have daylight I'll take a thorough look.
If anybody can give me a quick couple of things to look for I would appreciate it. Otherwise I'll go step by step to check for fuel, spark, etc..
Jack
1995 e320, 194k.