Ian manages to sabotage the Daleks bomb, while the Doctor turns the Roboman on the Daleks.
"Flashpoint" is an excellent conclusion to the story. There's some very nice model work, and I particularly enjoyed William Russell's performance.
However, the best part of "Flashpoint" is the final scene between William Hartnell and Carole Ann Ford. The Doctor's final speech to Susan is touching, and brilliantly performed by Hartnell; it's probably his finest moment on the show. Susan's departure is probably the best handled companion exit in the history of the show.
Overall, The Dalek Invasion of Earth has lots of ups and downs. "The Daleks" and "The End of Tomorrow" are disappointing in comparison to the other episodes. Richard Martin's direction is inspired in some places, but horrible in others. Jacqueline Hill is unfortunately sidelined for most of the episodes, and the cynicism of Jenny and Carl Tyler gets grating after a while.
However, there's a reason this is one of the best remembered episodes of 60s Doctor Who. It's tightly paced, with plenty of memorable imagery from Terry Nation. And then there's William Hartnell's wonderful performance.
A true classic. "One day I shall come back. Yes, I shall come back. Until then, there must be no regrets, no tears, no anxieties. Just go forward in all your beliefs and prove to me that I am not mistaken in mine".