Infiltration: The Set-Up!

is episode 171 of the original Naruto anime.

Synopsis
While on the beach, Anko, still unconscious, was being tended to by Ino. Meanwhile, Naruto spoke of his encounter with Isaribi earlier. The episode then moved to Anko's sudden reflection on her memories. She saw Orochimaru approaching towards her, telling her that the Hokage had found out about their experiments. Shino, Naruto and Ino decided to continue with their original mission: to protect the official payments and to capture the Kaima (Isaribi).

The group headed to Demon Island (Kikaijima), an island located in the Land of the Sea where supposedly the Kaima resided. Anko awoke and explained that the Kaima (the Demon of the Ocean) was a human who had undergone physical transmutations. Whilst they were talking, Yoroi and Isaribi headed underwater to Orochimaru's lair. Inside, Isaribi passed on the information relating to the official payments, and asked when she would return to normal. Yoroi told her that she was a prototype and that, when he was done collecting information from her, he would change her back. He then sent her to dispatch Naruto and the rest of the group, who had just arrived on the shore.

Shino, Naruto and Ino found themselves in an experimental laboratory with many creatures contained in test pillars. Isaribi approached from behind and triggered a trapdoor. The three Genin fell through the trapdoor, after which Anko appeared behind Isaribi with a kunai at her throat. Isaribi managed to escape, and left Anko locked in the room to face three large lion-like mutations. Anko made quick work of the three.

The rest of the team faced Yoroi Akadō, who was working for the enemy. Shino accepted his challenge while Naruto and Ino continued on to meet up with Anko. Anko, Naruto and Ino then found themselves facing Amachi and Isaribi. Amachi and Isaribi ran off just as Misumi Tsurugi appeared to face them. Ino used her mind manipulation jutsu to restrain him. Shino's opponent disappeared as the island began to collapse. Isaribi, Amachi and Yoroi escaped on a ship, leaving Team Anko to perish in the collapsing building. Naruto began to frantically search for an exit.