Agua Uno re-introduces the people who can turn into dolphins and vice versa first seen in the Lagenorhynchus story in the Theta Sigma series. There were two Theta Sigma stories about them, and one in the Unfinished Business series. This story tells about the fourth and fifth planets where the dolphin people went in search of a new life. Agua Uno and Agua Dos are advanced societies who have space flight and technology. They have split between land and sea dwelling, but remain on good terms with each other.

This is Davie’s first opportunity to test what he learnt from his great-grandfather – that he would inherit the name of Doctor. This time, he is only ‘borrowing’ it. He uses the influence to get into the important party and to meet with the Magister of the city. Later, though, he has to prove his worth as they are plunged into the kind of drama The Doctor would take in his stride. And of course, he and Chris find their own way of saving the day. They don’t do it exactly as The Doctor would do. But they know that they are not meant to. They do it their own way.

http://www.pearsecom.co.uk/thetasigma/09lagen.htm
http://www.pearsecom.co.uk/thetasigma/16%20sea%20life.htm

http://www.pearsecom.co.uk/doctorwho/67aquaria.htm