One Worth Betting On

is episode 287 of Naruto: Shippūden anime.

Summary
As Tsunade listens on to the events of what happened to A, Karai, and Nigai, who had stolen a scroll with ninjutsu from the Sugi Village, she realises the nature of the insect and that it was also inside of A. After explaining this and having A make a promise to her, Tsunade catches and destroys a bug which had been hovering near A for some time — unbeknownst to them that the Nokizaru Group had been using it as a method to spy on them. Preparing to operate, Tsunade has her pupil Shizune lead the surgery while she oversaw it. Though A initially protested, believing that Tsunade should perform the surgery, the Sannin allays her fears somewhat. As Shizune, aided by Amai begins the surgery, blood is splattered on Tsunade. Still haemophobic, a terrified Tsunade excuses herself from the room. Seeking an explanation, Shizune tells the two of Tsunade's two great loves and loss which led up to her current state. Hearing this the Raikage states that he would not have placed the lives of his subordinates in the hands of someone in that mental state, an indignant Shizune speaks out against his chastisement of her master, throwing the extracted exploding bug at his feet. Meanwhile in present time, Naruto and B continue to the battlefield while A and Tsunade continue the journey back to headquarters.

Trivia

 * While talking about Nawaki, Shizune mistakenly states that he died in the Third Shinobi World War, while the real time of his death is unknown.