The basic premise was that you were some sort of thief who wanted gold. Lode Runner is sacred, it is the seminal Virgin Mother Mary Convict of side-scrolling arcade games. Hell, it was one of those games that defined what PC Gaming would become.
There were about 100 levels of thievery and fun. The gameplay was fast, strategic, nail biting, and in all ways kickass. Back then it simply did not get better than Lode Runner. I've been a Lode Runner fan since it originally came out (in the prehistoric 80's) and I played it on a dowdy old Macintosh 512K.