Penny has been kidnapped and locked in a magical cage - as has Marina. They’ve been captured by Daniel - a Horomancer. A rare magical talent based on manipulating time. And he’s captured them both because they’re outside their actual timeline. They don’t belong in timeline 40 and their presence there is making time magic futz. He insists it isn’t personal (and Marina is clear that being locked in a cage is always personal).
He doesn’t listen to counter arguments and he uses his time magic to zap them all to timeline 23… except that this timeline has no magic so the cages fall and Penny punches Daniel unconscious. While he has no wish to release Marina since she is made of evilness and has just one overarching goal (be reunited with her girlfriend now she knows enough about now to actually not screw up. And though I really want to see more same-sex relationships I also kind of think this woman need to run, run for the hills!). But Penny releases her because she claims to know how to use the timeline jumping device
She’s lying. She tells Penny that she really should remember to trust his instincts about her in future. She is a terrible person.
They switch time lines but because she doesn’t know what she’s doing they end up in a time line where magic users are hunted down by law - thankfully we don’t delve into this very very tropey storyline. They decide they need advice on how to use this device and go to find this timeline’s Daniel and seek his advice. He is thrilled to see their more developed time magic and calls his mother, the founder of the Horomancy… who then collapses
Penny and Marina flee with his devices to communicate with the past and his mother’s notes and between the two they patch together some information: one of the core elements that Sonia used to develop time magic is a substance that basically causes time related brain damage - which she counters with watches that use time magic to keep their minds safe. Unfortunately Penny and Marina being outside their timeline is disrupting time magic - hence why Sonia collapsed. Her shield is no longer working
Penny realises that this is why Daniel is so eager to get them out of Timeline 40 - because their presence is killing his mother. Penny is horrified and insists that they cannot return. Marina, of course, doesn’t care. But Penny is the Traveller and the one able to zap away…
...to a white room. A room between life and death where he is pulled into a meeting but… Penny 40. Yes the Penny now working for the Library from the original Timeline - a much less fluffy, happy Penny with a whole lot more hard edges. He has a simple message - it’s vital Penny 23 return to Timeline 40: yes Sonia is going to die, but it’s too late, she’ll die anyway. Penny 40 is totally impatient by Penny 23’s emotional sadness and really really wants him to just get on with things. He insists that there’s something much much much bigger at play than just Sonia and Penny 23 must return
He also insists that this is Penny 23’s storyline now, and dismisses his guilt over taking Penny 40’s space. Again, he has no patience for this emotion - and it is really well done how these characters are very similar but fundamentally different. Often when the same actor plays two characters those characters are extremely different from each other (look at the Acting Superhero, Tatiana Maslany in Orphan Black) but it’s a brilliant change to see these characters be very similar but still have fundamental differences. Their morality and outlook is very different but they’re both recognisably the same person
Penny returns to his timeline (with Marina) and waits for Daniel… he realises Daniel will do anything to get rid of them since his mother is on the line… soe he plants dandelion seeds from timeline 23 into timeline 40. Daniel will never find them all… getting rid of Marina and Penny won’t help him.