Black’s queen is about to get taken by the rook on d4, so it would be natural to think about moving it to safety; but Black can do better. Think about offense and notice the kernel of a discovery on the e-file. What target would the rook have if it were unmasked? It would be aimed at White’s king, and the check could be made a double with Bb4—if only the White pawn on e3 weren’t in the way. With the obstacle identified, be methodical in getting rid of it. Try capturing something the pawn protects. It guards the rook on d4, which Black can take with QxR. Now if White replies e3xQ the e-file has been opened for the double check Bb4++. White then has to move his king to d1, permitting Black to execute the standard mate: Re1#, cutting off the king’s flight squares on the first rank and on the e-file while the bishop protects the rook and cuts off d2.