When the Tom Baker episodes were first syndicated to American commercial television, the distributors, Time Life, added a series of voice-overs before every episode in an attempt to try to "explain" what was happening to the American audience.
Right after the opening titles to each story's first episode, a series of clips from each episode of that particular serial would be shown, narrated by the late Howard DaSilva. These clips would often include all the cliffhangers from that story. A short voice-over would also be added at the beginning of all the other episodes, though without any clips. All of this should be more familiar to buyers of the earlier R1 DVDs, as they were included as extras. BBC Worldwide's decision to make all the DVDs uniform in all regions means they will no longer be included on future releases.
I have transcribed the voice-overs from certain Part Ones (ie all the ones I've got). I've included the Part Ones from the stories already included on DVD in R1 for the benefit of those outside North America. To read them, click on the links below: