A large plume of whitesmoke and a ratteling noise occurred before the engine lost power. What is the problem?

A few more details would be useful.
What make, model and fuel.
Any other symptoms, no matter how small..

The engine likely overheated, blowing the head gasket, allowing the coolant to burn in the cylinders (white smoke). Repairs will be expensive.

Internal grenade explosion of the internal combustion engine.