Unfortunately I struggled with this. It's clearly one of those books that was written because the author had to write something. Quite frankly, it's a bit of a mess and doesn't do the name Spider Robinson any justice at all. It contains a few callahan's stories, some other none callahan's stories and an awful lot of gumph in between these stories which is simply the author filling-in... a great deal of filling-in in fact.
My advise would be to simply scip this one and go straight onto the next. I wish I had.