puzzle No. 270

Black to play. This position is from Bacrot-Ivanchuk, Thessaloniki Grand Prix 2013. This was the scene of Ivanchuk’s only success. What is the key move? Answers to me at The Spectator by Tuesday 18 June or via email to victoria@spectator.co.uk or by fax on 020 7681 3773. The winner will be the first correct answer out of a hat, and each week I shall be offering a prize of £20. Please include a postal address and allow six weeks for prize delivery.
 
Last week’s solution 1 Rxe5+
Last week’s winner David Bennett, Hove, Sussex