'The Doctor arrives on Christmas Eve in an Australian suburb threatened by bush fires. He enlists the help of a cynical and bitter man, disillusioned for a number of reasons: his house has just been burnt to the ground by the approaching fire; his wife, Sarah, has recently left him; he is at the home of Sarah's sister Lucy and her husband Jim with whom he has fallen out. The Doctor contrives to build a complicated machine, powered by the TARDIS, which puts out the fire as Christmas Day dawns. Most of the water comes from the leaky TARDIS swimming pool. As he builds the machine the Doctor seems preoccupied with helping reconcile his helper with his in-laws, but more than this with his own people who allowed a firestorm to destroy a whole world. After the Doctor mysteriously vanishes it transpires that no one knew who he was or where he came from.'
[The Doctor is the Sixth Doctor.]
Source: drwhoguide.com (http://www.drwhoguide.com/whotrip18.htm). Sighted 20/5/11