In "The Forest of Fear", the Doctor and his companions are freed from the Cave of Skulls by Old Mother - who fears the violence that will result when the tribe rediscovers how to make fire. They are pursued into the nearby forest by Za and Hur, who hope to force the Doctor to reveal the secret of fire to them. Meanwhile Kal continues to harden his support within the tribe.
There's a greater sense of urgency about "The Forest of Fear" that pushes it beyond the level that "The Cave of Skulls" had reached. The TARDIS team all get the opportunity to show their characters a bit more broadly, and certainly this episode ups the conflict between them. The Doctor wants nothing more than to escape to his TARDIS, and when Za is badly wounded in the forest it's Barbara who acts as the team's moral centre and insists they abandon escape to administer first aid to him.
The Doctor's reaction to Barbara is highly unexpected. He shouts, and rants, and sulks, and obstinately refuses to assist his companions in saving Za's life. At one point he even sneaks up on the unconscious Za with a rock, clearly intent on bludgeoning him to death before Ian stops him. It's a far cry from the good-hearted crusader we think of today. In the context of Doctor Who as a whole, it's scenes like this that make me really enjoy "An Unearthly Child". The Doctor wasn't born. He was made, slowly crafted into the character we see today by contact and experience with his human companions. Before he begins travelling with humans he's as callous and callow as any Gallifrey-based Time Lord we later meet.
With a stab of Kal's dagger Old Mother (Eileen Way) becomes the first casualty in Doctor Who history. It's a surprisingly blunt death, one made possible I suspect by the episode's black and white visuals. The image of Old Mother lying lifelessly on the floor of the Cave of Skulls, blood trickling from each side of her mouth, is certainly softened by a lack of colour.
At the episode's conclusion, Barbara's assisting Za has led to the group's recapture. Kal glares at them with what looks like murderous intent. Next episode: "The Firemaker". This is a great episode, and I really think Doctor Who fandom at large needs to re-evaluate this serial. It may not quite match the style of the series beyond this point, but it's a marvellous slice of early 1960s television drama. Three for three: 100%.