Double jeopardy bars a retrial on a substantive offense when jurors reached a verdict on the substantive offense but deadlocked as to an enhancement. Sullivan was charged with robbery and assault likely to produce great bodily injury (GBI). It was also alleged that he inflicted GBI in violation of section 12022.7. The jury reached a verdict on the substantive assault charge, but was unable to reach a verdict on whether Sullivan had actually inflicted GBI. The trial court concluded that it could not take a verdict on the substantive offense without the enhancement, and declared a mistrial. Following a second trial, a new jury found Sullivan guilty of the assault, but found the GBI enhancement not true. The appellate court reversed the conviction. The trial court’s discharge of the jury in the first case without a verdict prevented a retrial. Once jeopardy has attached, discharge of the jury without a verdict is tantamount to an acquittal and prevents a retrial. Because the jury reached a verdict at the first trial, the trial court should have received the verdict on the assault charge and declared a mistrial only as to the great bodily injury enhancement. Because it did not do this, Sullivan’s double jeopardy claim was meritorious and reversal was required. Sullivan’s counsel was ineffective for failing to advise him to assert a plea of once in jeopardy. There could be no tactical reason for not raising a plea of jeopardy in the second trial.