MAJOR SPOILER ALERT!!!!!
The book opens up with the spying on Voldemort by muggle Frank Bryce. He manages to hear as far that Voldemort's deepest desire was to murder a boy named Harry Potter, whoever he was, and he had killed in the past with no remorse-before he was discovered and killed himself. The boy who was also spying, though unconsciously, and in his sleep, the very person who was target of Voldemort's murderous desires, was not discovered.
Harry became incredibly worried at this vision and that his lightning scar, mark of the first, but certainly far from last, attempt at slaughtering him by Voldemort. Was Voldemort growing stronger, as all signs seemed to indicate? Harry didn't dwell on it for about two days (spent by the Weasleys and watching the Quidditch World Cup). But at the end of that he was seriously alarmed and alert, because Voldemort's sign, the Dark Mark, had appeared again after thirteen years, after a riot which was heavily suspected of being made by the remainder of the Death Eaters (Voldemort's supporters). His fears weren't baseless either, as somebody had put his name into the Goblet of Fire against his will, and Alastor "Mad-Eye" Moody, dulusional ex-Auror thought someone had done it to get him killed in the process.