VLOOKUP reference

I am using the vlookup to retrieve values from a 2nd Workbook/Worksheet (I will call this the Reference workbook)

The reference workbook has multiple sheets.

My primary workbook has a column that has the corresponding values for the sheet to be used for that lookup.

So, my VLOOKUP command is: =VLOOKUP(H2,[REFWORKBOOK]WORKSHEET'$A$1:$D$2000,4,FALSE

I would like to substitute "WORKSHEET" in this formula with the value of Column E. I have tried the INDIRECT function, but get an error:
=VLOOKUP(H2,[REFWORKBOOK]INDIRECT(E2)'$A$1:$D$2000,4,FALSE

Any way I can do this?

Thanks Much