Death of the 5th Doctor. He did what he could to save his companion and in the end, the poison in his system was to much for him to survive. How fitting that his last word was calling out to Adric, showing his regret that he wasn't able to rescue him in time. Still brings a tear to my eye. This one still remains my favorite regeneration scene. Goodbye Doctor #5, and thank you.
He held back his regeneration long enough to save his companion. I loved the progression of the Doctor in this story. Wonderfully acted by Peter Davison.
Peter Davison would go on to say that if all his stories were like this one, he would have stayed on longer.