To complete this activity, you first have to identify the kind of style that Shelley employs in her original and its various aspects. Shelley structures her narrative through a framing narrative, as the account of Victor Frankenstein is sandwiched or framed between the story of Walton and his own voyage into the unknown. If we consider the kind of langauge that is used, we can see that it the level of vocabulary is not necessarily too sophisticated, but it clearly indicates the time in which it was written, as a number of quite elevated words are used.
As a result, if we put this together, the best way of writing a summary of this novel using the same kind of style would be to write it as a framing narrative trying to imitate the same register. I wonder if you could actually do this in a very clever way by moving the story into the 21st century, and having a scientist who is trying to unlock the human genome come across another scientist who has managed to clone humans with terrifying results. Such an updating would allow you to summarise the story in a fun way while clearly pointing towards the thematic relevance of this vital work.