Jetsetter, adventurer, and owner of a very unusual London bus, Lady Christina de Souza is travelling the globe and catching up with the rellies. First, a treasure hunt with her reprobate father in the Indian Ocean. Then, a flying visit to the Australian outback in search of a lost Great Aunt... But Sam Bishop and Jacqui McGee of UNIT are on her trail. As one reunion takes a dangerous turn, Christina has a hard decision to make – for the good of the family!