Create A Range Variable From Cell Text

Let's say I have cell A1 on Sheet 1 of Book 1. I need this cell to be a range variable for a macro in Book Two, but cell A1 varies from time to time (A1 this time, A7 next time).

In Book Two, I write "A1" as the contents of cell C3, for example. How do I turn that string into a range variable for use, not the containing cell? Since the cell needs to manually changed each time I run the macro, having it as a text field somewhere on my Book 2 Sheet seems the only simple way to identify it but IS there another way? Selecting it as the active cell and using another subroutine defeats the use of the macro.