Oh and I should say that my copy of Ringer was provided to me by Book Bridgr in return for an honest review.
Ringer is set a few months after Replica with both Lyra and Gemma having to get used to how their lives have changed. When Gemma overhears something she goes to warn Lyra to get out but the other girl was already leaving to follow after Caelum. Both of these stories are a lot more action-packed than the first book and they can be read either one after the other or in alternating chapters.