Drilling into stone wall with plaster on top
I have found mounting a scrap piece of wood to use as a guide helps drill through the wood and place the bit in the hole so you have exact alignment, use a couple of screws to hold the board in place not screwed tight but create a divot from at least 2 screws 3 is better. Now press the board tight and use your masonary drill bit (hammer drill will make this go much cleaner and faster so borrow one if you can).  usually you only need to drill in about a 1/8 to a 1/4" and the hole will then guide the bit. Remove the board and finish drilling the hole and then patch the divots. I have done this without creating the divots but I am a really big guy and will still usually create at least 2 so the board dosent shift.