Draco Malfoy (Tom Felton)’s Timeline and Summary

Draco goes to Borgin & Burke's with his mom to meet up with some Death Eaters. They're examining some giant cabinet together. Seems like an odd time to go antiquing, but to each his own, right?
Well, maybe it was more than that: When the kids are back at Hogwarts, we find out Malfoy has been playing with a similar cabinet hidden in the Room of Requirement. He seems to be practicing making things disappear and reappear.
He does a lot of skulking around the halls, and weird deadly objects intended for Dumbledore's hands keep showing up.
Harry puts two and two together and figures out (correctly, as it turns out) that Malfoy is responsible. He confronts Malfoy and accidentally nearly kills him, actually. Malfoy never admits to anything, but he does a lot of agonized crying.
At the end, the truth comes out: Voldemort gave Malfoy the mission of killing Dumbledore. Malfoy shows up to do the deed, but he has serious trouble going through with it.
So, Snape shows up and finishes the job. He had promised Malfoy's mother he would complete the mission if Draco was unable to, and so he does.