It is revealed that it was Fenric used the time storm that opened up in Ace's bedroom that brought her to Iceworld, which was the alien planet where The Doctor first met Ace (Dragonfire) and Fenric also opened the time storm that brought Lady Peinforte from 1638 - 1988 (Silver Nemesis) and that The Doctor knew all along.
Two of the Haemovores in part four are played by Sylvester McCoy's sons Sam and Joe Kent-Smith. Their scenes were cut from the transmitted version of part four, but were reinstated for the extended BBC Video version and the Special Edition movie-length version included on BBC Worldwide's DVD release of the broadcast version.
In the novelization, when Fenric kills Nurse Crane, he reveals that she was a Russian agent and had led the soldiers to the installation, which may explain how Millington knew that the Russians were going to steal the ULTIMA machine. This was not derived from any information given in the televised version.
The confrontation between The Doctor and The Ancient Haemovore was originally longer. It was scaled down when the episode overran.
This episode was watched by 4.2 million viewers on its original transmission.