"TOKYOMER" was officially recognized for half a year. In order to carry out MER in designated cities nationwide, Kitami (Suzuki Ryohei) is troubled by the issue of the second doctor who will replace Otowa (Kento Kaku) who left the team. The voices in the team that want Hina (Ayami Nakajo) to be promoted are also increasing, but Otowa insists that Hina should move on to the path of cardiothoracic surgery. Hina also feels pressure and worries whether she can replace Otowa. At this time, Aoto (Atsushi Ito) comes to MER as a supporting doctor. Aoto is a medical technician of the Ministry of Health, Labor and Welfare, just like Otowa. On the surface, he is dispatched as a second doctor candidate, but the Ministry of Health, Labor and Welfare has its own ideas. At this time, a collision between a large water bus and a houseboat occurred on the Sumida River. The houseboat, which lost control and carried many injured people, ran wild. Although the members of MER rushed to the scene, they could not enter because they could not board. And due to the fuel leakage inside the bottom of the ship, the possibility of explosion with many patients on board was discovered! Kitami and others carried out unexpected operations to save the abandoned people. That was a life-or-death challenge.