Excel 2007 : How to return a cell reference instead of a cell value

Does anyone know how to return the reference of a cell instead of it's value?
Specifically my problem is as follows:
In my spreadsheet, cell O4 references and returns the value from cell C4. In cell P4, I want to return the value from the cell that's one row down and one column left of cell C4. So I need cell P4 to call the cell reference instead of the cell value of C4, then manipulate the cell location to go one down and one to the left, and return that cell's value .. which should be the value of cell B5 = 18. So, cell P4 should return 18. Is there a way to do this?