"The Secret Behind the Underground Room" (地下室の秘密, Chikashitsu no Himitsu) is the 173rd episode of Boruto: Naruto Next Generations.
Summary[]
Boruto and Sarada visit Mia to return Anato's ring and tell her about the circumstances behind the mission. Victor guides the Land of Valleys Daimyo around his facility and shows him their work healing patients with terminal illnesses with the Hashirama Cell. However, Konohamaru and Mugino, posing as his bodyguards in disguise, release him from a genjutsu which concealed the actual human experimentation Victor was conducting. Victor initiates his plans which results in a plant resembling a Divine Tree blooming into his facility, causing an earthquake which alerts Boruto and Sarada, who rush to the scene.