A sudden accident shatters the everyday happiness two couples had always taken for granted — and exposes a secret one of them kept hidden for years.

Itsuki reveals he saw Azusa and Mitsuru together on "the third Friday." Sakiko wants to believe her husband, but begins investigating their secret.

As their investigation stalls, Sakiko and Itsuki bond over shared frustration. A call from the police leads them to retrace Mitsuru and Azusa's steps.

The discovery of two sets of tickets forces Sakiko and Itsuki to confront the possibility of an affair. Sakiko then finds a new clue on Mitsuru's phone.

Sakiko follows Mitsuru's trail all the way to Nagano, while an unexpected guest from Azusa's childhood pays Itsuki a visit.

A sudden return brings Sakiko, Itsuki and a familiar face together for the first time. As truths emerge, Sakiko reflects on her life with Mitsuru.

Sakiko and others are asked about their relationship by Mitsuru. While the truth of the third Friday is told, Jitsuo receives a diary left by Azusa.

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