Who was Marcus's guest in the episode when Rufus's guest was Rory McGrath?
CREATE TABLE "table1_19930660_2" (
  "episode" text,
  "first_broadcast" text,
  "rufus_guest" text,
  "marcus_guest" text,
  "winner" text
);
SELECT "marcus_guest" FROM "table1_19930660_2" WHERE "rufus_guest"='Rory McGrath';