I understand the events as follows:
1) Sirrus found a way to break through the wall in Spire (thanks to his vibrating rocks/bombs thingies), allowing him to link to Tomahna, where he had to make some door explode, which is what made the bridge collapse.
2) Yeesha ran, and managed to link to Haven. She passed through the small door (used normally for food, clothes, etc.) and got on the beach.
3) Achenar found her. Sirrus arrived, made everything explode again, Achenar tried to protect Yeesha, Sirrus knocked him unconscious and took Yeesha back to Tomahna.
4) Sirrus forced Yeesha to show him the linking book to Serenia, and tied her up there.
5) Achenar woke up, and followed them all the way to Serenia.
Which is basically what you said, I think.
(and I bought the soundtrack from
there)
