The unwelcomed visitor was previewed in the last episode before this episode.

Episode 348

Sakura notices someone while she was picking medical herbs for Sasuke. She went to she who was and found out it was Haku, but she didn't recognize the other person who happened to be Shiroshi. Shiroshi introduced herself as Yūhi Satō's old team member and an ex-member of the Yūmi Satō because she left yesterday and was almost killed for doing so. Shiroshi later says that she and Haku must go because they have to revive others. Sakura tells Naruto this and Naruto says, Haku?! 

Preview: Love at first sight

Sasuke says he will go to Ochimaru and tell him about Yūmi Satō since Sasuke knows he will help. There Sasuke finds Karin lost and she later senses Sasuke and greets him. Sasuke tells her about it and she says that Ochimaru moved and she now usually gets lost and walks until she finds either his, Jugo's, or Suigestu's chakra and folllws it.