2003 Ford Ka Overheated Engine

So i was just coming home from about a 1 hour journey. just as i pull in to my drive the red warning light for temperature turns on. so i park up. turn off the engine and i can hear a kettle whistling sound from the engine, and what appears to be a small oil leak but only for a few metres from the car (like it only just started leaking). I open the bonnet and a plume of white smoke goes everywhere. and water in the overflow tank is boiling. I released some of the pressure and let the car cool for about half an hour. i then checked the oil, the oil is at a good level and looks normal, no cloudy effects, but at the top of the dipstick was a few droplets of what looked like water. as if it had condensed at the top of the stick. So i checked the overflow tank for oil but it didnt appear to have any in it. There was some leakage under the car directly below the engine of oil / coolant im not too sure but only a few drops on the floor.
I ran the car the next day as i was pretty desperate to get to work, and as i was idle waiting in traffic, in 1st with clutch and brake down, the revs repeatedly dropped and came back up again over and over about 5 times but it didnt cut out. as soon as i started moving off again it was all back to normal and havent had this problem since. Water/coolant/oil levels are still normal 2 days after and im not having any issues rigt now when driving, but i assume somthing had failed and needs repairing?