Q: Engine makes a high purring sound and won't turn off when key is taken out.

For the past few weeks, my truck has had some very minor issues, but has run just fine. Yesterday on my way to work, the car failed to start the first two times I turned the key (as if the battery was dead), and finally it started the 3rd time. I was in gear, with my foot on the clutch, and the engine was making a high purring sound. After hearing this, I turned the car off (turned the key), but the engine did not turn off, and began to clunk. When I put the car into neutral, the clunking continued. When I put the car back into gear and took my foot off the clutch, the engine stopped, but then every few seconds it would oscillate and push the car a foot forwards. After having fits for about 15 minutes, smoke started coming from the bottom left side of the engine (as if you were looking into the hood). After doing the lurching thing for about a minute, the smoke died down and the engine died/turned all the way off. I have yet to turn the car on again. What should I do?

My car has 82000 miles.
My car has a manual transmission.