The thestrals landed outside the visitor's entrance to the Ministry of Magic. They split up into groups, and crammed into the phone booth. They exited, and ran full speed to where the battle was taking place. Harry saw nearly fifty Death Eaters, along with vampires, hags, ghouls, and dementors, fighting against members from the Order of the Phoenix. Harry saw Kingsley and Tonks fighting, along with Brenda, Linda, and Fluer Delacour, who Harry didn't know was in the Order. She must have been a new arrival.
Dumbledore was fighting against three Death Eaters at the same time, while others were fighting against the others. Harry drew out his wand, pulled the hood over his head, and yelled out "Expecto Patronum!" Suddenly, all of the dementors in the room were being charged by not only a stag, but also an otter, a lion (Ron's Patronus), and a falcon (Ginny's). The dementors fled from the room, and Harry turned to see the D.A. holding their wands upright. He split them up into their pairs, and told them to stick with a member of the Order of the Phoenix.
Harry and Ginny ran up to help Professor Rasbutinoff. He was dueling with Antonin Dolohov and Rasbatan Lestrange, two of the Death Eaters who had escaped from Azkaban. Harry and Ginny immediately set upon them with the Impediment Curse. Together, the three dueled against many Death Eaters and other creatures.
The rest of the D.A. was fighting a winning battle. They had helped the Order of the Phoenix ward off many Dark creatures and wizards. The battle was coming to an end. The Death Eaters collected their fallen, and Disapparated.
Harry looked around the room. He saw that they had lost some members of the Order. Hestia Jones, Elphias Doge, and Emmeline Vance. Three of the remaining members of the original Order of the Phoenix were dead, and others were injured.
Harry collected the D.A. as fast as he could. Aside for a few minor injuries, the group was unhurt. They hurried out of the building, before they could be spotted by any Ministry officials. They found the thestrals waiting outside, and hopped on, flying back to Hogwarts.
It turned out that Malfoy had not created mayhem at the ball. In fact, he had been up in the hospital wing, suffering from an unknown illness. Later, Seamus confessed that he didn't want to attack a school prefect, so he had slipped a Skiving Snackbox into Malfoy's punch. However, he hadn't given him the antidote piece. Malfoy would be vomiting for hours.
Harry called an emergency meeting of the D.A., and they discussed the night's events. As they were all leaving, Dobby the house-elf came running in to Harry. "Harry Potter, sir, Professor Dumbledore wants a word with you, sir." Harry headed off to Dumbledore's office.