Harry Potter and all characters, etc. belong to J.K. Rowling, not me.
What if Draco was Competent?
This is the darkest fanfiction I've ever written. You have been warned. It begins with an excerpt from Harry Potter and the Half-Blood Prince.
"Petrificus Totalus!"
Without warning, Malfoy pointed his wand at Harry, who was instantly paralyzed. As though in slow motion, he toppled out of the luggage rack and fell, with an agonizing, floor-shaking crash, at Malfoy's feet, the Invisibility Cloak trapped beneath him, his whole body revealed with his legs still curled absurdly into the cramped kneeling position. He couldn't move a muscle; he could only gaze up at Malfoy, who smiled broadly.
"I thought so," he said jubilantly, and he stamped hard on Harry's face. Harry felt his nose break; blood spurted everywhere. That's from my father." He then pulled the Invisibility cloak out from underneath the Chosen One. "Give my regards to the Dark Lord." With that said, he pointed his wand at Harry's glasses. "Portus," he incanted, and a moment later, Harry disappeared, being pulled by a portkey.
Draco quickly made his way to the carriages after pocketing the cloak and got into Hogwarts with no problems. After watching Dumbledore give his speech and sit down, he waited for the headmaster to give his full attention to his plate, then Malfoy quickly pulled his wand out, pointed it at Dumbledore and whispered, "Avada Kedavra!" sending a green beam of light that hit the former headmaster in the side of the head as he was placing a fork full of roast beef into his mouth. The fork dropped just before Dumbledore's head landed on top of it, on the plate. Draco about jumped off his seat and began running toward the entrance hall in the silent shock.
McGonagall pointed her wand at Malfoy just before he reached the doorway, only to be stunned by Snape, who was forced to keep his unbreakable vow. The head of Slytherin then made his own way out of the Great Hall, shielding himself because he knew nobody there would use a spell that went through shields.
As soon as Draco was in the Entrance Hall, he put the Invisibility Cloak on and made his way toward the door, knowing that it was locked and he couldn't open it. He'd simply wait for someone else to open it. He thought it might be an hour before the Aurors did that, however, Snape ran toward the door with a few members of the staff following him. The Potions teachers performed a spell on the door, causing it to open and Malfoy made his move. He got in front of Snape and made his way out of the school while Severus's shield finally was broken by Flitwick's spellfire. Draco didn't look back as he ran; therefore he didn't notice Snape falling, stunned and bound.
Malfoy stood perfectly still near the gates while the staff unsuccessfully searched for him. He was rewarded after fifteen minutes when the gates were opened to allow the Aurors inside. He quickly snuck through, escaping the wards of Hogwarts. He then created another portkey and vanished.
"Welcome, Draco, greatest of my followers," greeted Voldemort. "In one hour you have accomplished what all my other followers have been unable to do in years. You have killed Dumbledore and sent me this wonderful gift." He then indicated Harry, who was locked up in a cell. "I thought I'd allow you to have some fun with him before I kill him. Enjoy."
I hope you liked this story. The only thing it adds is that Bellatrix taught Draco how to make portkeys while she was training him in the Imperius curse, Occlumency and anything else she taught him.