3NT was forcing asking for outside strength. 4♣ showed a club card and 4♠ denied outside strength. 4NT was Roman Key Card Blackwood 1430, looking for the ♠K. 5♦ denied the ♠K, so here you are in everyone’s favorite contract, 5♠.
West leads the ♦J. Plan the play. Spades are not 4–0.
(1) Jacoby; game-forcing raise.
When East doubled 4♣, you liked your hand because partner’s strength figured to be outside of clubs. At least, that’s what you’re planning to tell partner if things go awry.
West leads the ♣J. Plan the play. (Both follow to the first spade.)