While Time Heist is a forgettable episode, Psi and Saibra are such well drawn characters that it redeems a dusty plot. The actors play this pair with both bravery and frailty and the hints given of compelling backstories make one want to follow them off the TARDIS and into their every day lives. It does not appear they were written with a double act in mind but they come close to fulfilling that role. Too often we only see characters in terms of their interaction with the Doctor but these two are fascinating to watch when circling around each other. Psi and Saibra are examples of how to write people capable of independent thought. They do not need the Doctor to make decisions for them. They are not satellites or slaves to another person's whim. They are two people caught up in events beyond their control but they are never subsumed by the Doctors charisma. They each shine their own light.