Everyone knows a computer's "undo" command will erase a mistake.  Thanks to a device called the Unner, middle-schooler Gib Finney can do the same thing -- in real life.  At first he thinks this is better than winning the lottery; he'll never flunk another test, never lose another bet, never strike out again.  But after a terrible traffic accident, Gib must decide which events in a two-day period he needs to change to prevent disaster.  Was the key when he and his friend Ash saw signs advertising a carnival?  Or when he argued with Rainy Frogner about their science experiment?  Or when he shot a spitball at his math teacher?  Gib soon learns that some things are more worthy of "unning" than others, and that some events may be impossible to change at all.

 Weaving together thought-provoking questions and a tense plot, this fast-paced time-travel fantasy portrays one boy's struggle to escape a terrible fate.