What is the irony in Tom's escape plan for Jim? In the same way, how might you say that the entire voyage down the river is ironic?

First of all it is ironic that Jim was free man already. He had been released by Miss Watson before she died. Tom's escape plan was overly elaborate to the point of ridiculous. It could have been achieved much easier and Huck knew it. I think the voyage down the river was ironic because it took two outsiders (orphan and a black man) to expose the hypocrisy and injustice of all aspects of "civilized" Southern white society of the time.