Try...

B2, copied down:

=SUMPRODUCT(SUMIF(INDIRECT("'"&$D$2:$D$5&"'!D:D"),A2,INDIRECT("'"&$D$2:$D$5&"'!F:F")))

...where A2 contains the 'concept' of interest, and D2:D5 contains your sheet names.

Hope this helps!