vlookup using 2 lists

I am looking to invent a function which will look up a unique reference from a list. If it does not find the reference in the first list, it will automatically vlookup the reference from a second list. I will use FALSE to find exact match.
Any ideas?
Was playing around with IF nested and that might work. Any help would be greatly appreciated.
Ta. Colmodoc

Here is a basic template of what you want to do I think

Nice one. Came up twice in two different contexts & your help is most appreciated. Just for my own amusement I'm working on that to look up 3 lists but my limit of 3 arguements in the if function is giving me some work.
I've another prob re linking/filling down and transposing that I'm about to file.
Thanks