The Message Bible:
John 13:21 After he said these things, Jesus became visibly upset, and then he told them why. "One of you is going to betray me."
22 -25 The disciples looked around at one another, wondering who on earth he was talking about. One of the disciples, the one Jesus loved dearly, was reclining against him, his head on his shoulder. Peter motioned to him to ask who Jesus might be talking about. So, being the closest, he said, "Master, who?"
26 -27 Jesus said, "The one to whom I give this crust of bread after I've dipped it." Then he dipped the crust and gave it to Judas, son of Simon the Iscariot. As soon as the bread was in his hand, Satan entered him.
"What you must do," said Jesus, "do. Do it and get it over with."
28 -29 No one around the supper table knew why he said this to him. Some thought that since Judas was their treasurer, Jesus was telling him to buy what they needed for the Feast, or that he should give something to the poor.
30 Judas, with the piece of bread, left. It was night.
I've read several explanations as to why the other disciples didn't know what was happening, but none are satisfactory. Oh well, looks like I'll have to ask them when they come back to life.
Sylvia