any ideas, just fire something at me as i'm stuck

Just got back from picking the car up, had to get towed home, but i sat waiting for my mate to turn up for 20 minutes the entire time the car was ticking over just fine, i know if i had tried to drive it, it would have died so left it running, mate turns up and starts towing me, i have it in neutral and not touching the gas, car just died as soon as it moved with the tow??????