On Sheet4 make a named range (A1 to A3) called MySheets containing Sheet1, Sheet2, Sheet3.
In Sheet4!E5 put next formula. Remember that this is an Array-formula. (Ctrl-Shift-Enter)

PHP Code:
=VLOOKUP(D5,INDIRECT("'"&INDEX(MySheets,MATCH(1,--(COUNTIF(INDIRECT("'"&MySheets&"'!A2:A20"),D5)>0),0))&"'!A2:B20"),2,0)