Sally is violently separated from her father when a scientific demonstration they're attending goes horribly wrong. She is thrown back in time, and has to live her entire eighteen years over again, not knowing if her Dad has survived the disaster or was killed by it.
They are finally reunited, but then discover that someone else was thrown back even further. Sally, now calling herself Lucy, volunteers to travel into the future to obtain the technology they need to rescue the young man. But authorities in the 2080s require her to carry out various missions before she can get the help she needs. She eventually rescues the young soldier, returning him to the 1970s.
Some weeks later Minister Mary, who befriended and helped Lucy in the 2080s, travels back in time for a visit. An accident causes Mary serious injury, but involves Lucy and her Dad in more adventures, first in the 1800s, then the 1970s. MI5 finally recognises Lucy's unique abilities, and gives her the recognition she deserves, while in the 21st century she is made Minister of Temporal Affairs.
The book is 106,000 words approximately