In the last episode Okabe undoes his last time-line change, the one where he stops Suzuha from travelling back in time before the rain storm damages the time machine. While Okabe and Kurisu works out part of the logic behind the time lines and why Mayuri keeps on being killed, it was Suzuha which given the last clues to work out most of the puzzle. They, as of yet, have not worked out how to stop Mayuri from being killed yet. After the tragedy of Suzuha trip in time is revealed, Okabe in an impulse act stops his earlier time-line interference. These results in Suzuha travelled back in time, while never knowing who her real father is, and even mauyi's death is delayed. This is the last clue and Okabe and Kurisu decide the solution is to un-do all the previous time-line changes. This episode covers the faris time-line change and, as with the last episode, all the standard tropes are rolled out and they all work. Once again, if you are engaged with the characters, even when you know the trope is decided to get a specific response, you can't help yourself. Another excellent episode.