As we mentioned in the previous mishnah, this mishnah and the ones that follow all deal with the components of the conditions of the kesubah - those conditions that remain fully in force even if they are not actually written in the kesubah. Our mishnah addresses the husband's obligation to redeem his wife if she is taken captive and requires ransom.
The words of the mishnah:
"Lo katav lah: im tishtava'i efrekinach ve'otvinach li le'intu" - even if he did not write in her kesubah that if she falls into captivity he will redeem her and restore her as his wife.
"U'v'chohenes: ahadrinach li'medinatich" - and in the case of the wife of a kohen the wording of the condition is different: I will redeem you and return you to your homeland.
The law of the wife of a kohen:
The wife of a kohen who is taken captive becomes forbidden to her husband unless we know otherwise, since we must assume, sadly, that she was violated by her captors, and once she has had relations with a gentile she is no longer permitted to her husband the kohen. Even in this tragic situation, however, the obligation of redemption has not lapsed, and therefore the wording of the condition for the wife of a kohen is "ahadrinach li'medinatich" - I will redeem you, but I will return you to your place and to your father's house, since I can no longer remain married to you; in any event, I will fulfill my obligation to redeem you.
Even if the husband did not write these conditions in the kesubah, he is obligated to redeem his wife, for this is a condition of the court - a condition that exists by the authority of the court, whether it was written or not.
In summary: In this mishnah we learned of the husband's obligation to redeem his wife from captivity and restore her as his wife, and the special wording of the condition regarding the wife of a kohen - who becomes forbidden to her husband because of the concern that she was violated in captivity - in which the husband undertakes to redeem her and return her to her homeland. This obligation remains in force even if it was not written in the kesubah, because it is one of the conditions of the court.