Roots: Arabian Nights, particularly the 'orphan' stories Ali Baba and the Forty Thieves and the tale of Khurafa. Clements based Amy's learning patterns on Chinese SF author Wei Yahua's novella Conjugal Happiness in the Arms of Morpheus (Wenrou zhixiang de meng) and its sequel. The Importance of Being Earnest ("a handbag?"). The Djinn ship's computer 'speaks' Farsi.
Goofs: It seems churlish to argue that to the best of scientific knowledge there is no such thing as "an atom of snot", but thanks for the mental image anyway.
Technobabble: Super-condensed heavy gold is the perfect catalyst for a spacecraft's warp manifold as it does not gain weight with the reduction in mass.
Removal of the lifeform of an organic host of a Key segment from the continuum will cause a temporal quake.
Dialogue Triumphs: "...They're professional farters, Lord Cassim." "-That's a profession?" "Indeed it is." "I despair of the arts..."
The Doctor and Nisrin: "Don't call me that" "'Master'?" "Yes, it's - unsettling."
The Guardians meet: "So, you are my adversary - my other half..." "I'm sorry, does that mean we're married?" "I hope not!" "So do I..."
Continuity: The Guardians' powers over time wane as it recedes, effectively imprisoning them in mortal bodies. Both Guardians have had legions of minions at work for millennia, but over this time their power has diminished, as has their power to command large groups. Eager for its energy, the Black and White Guardians are both searching for the two remaining segments of the key to Time, which are beyond their reach, being already held outside time.
The Djinn are a race of blue-skinned travelling collectors who'll buy and sell anything, going from world to world in search of profit. Their weapons fire an electrical charge and their warp ship (a long-range trading orbiter) comes equipped with basic service robots not programmed for security.
Links: Enlightenment (Tegan's tiara jewel, the Doctor recalls the Black Guardian's treatment of Turlough)
Q.v. 'The Guardians and the Key to Time', 'The Guardians and the Grace'
Location: In and near Dunqula, 9th century Sudan, the time of the Caliph al-Mutawakkil
The Bottom Line: "What did your last slave die of?"
Inventive. And Clemet's dedication to Arabian astronomy is laudable; it's a shame that the overly-comic treatment of the Guardians removes their threat (albeit to increase the forthcoming mystery of the Grace). On the other hand, the prospect of the Black Guardian as the Doctor's de facto companion is an idea too good to resist. And on that note, it's a 'Simsim' from us.