She is played by Rekha Sharma.
Not much is known about the Doctor but that she is from the Mountains Area and became an intelligent scientist.
In The 48, she comes into the hospital section of Mount Weather and greets Clarke, who is sitting on one of the beds. She then takes Maya to be decontaminated after Maya has a brief conversation with Clarke.
In Inclement Weather, she tampers with the gunshot wound on one of the guardsmen to make it look like an arrow wound just before showing Clarke the body. She later tends to Clarke's wound after she purposely reopened her stitches to get back into medical.
In Reapercussions, she is seen in the Harvest Chamber, where the Grounders are being drained of their blood, and her being there forces Clarke to hide in Anya's cage in order to keep from being spotted by her. She is also briefly seen at the end of the episode doing a Grounder check. When she comes across Lincoln, she says to take him to "The Cerberus Project".
In Human Trials, she is first seen at the quarantine room helping Maya who is suffering from severe radiation burns. When Jasper and Monty arrive, they see that Maya is in poor condition, and Jasper wants to help. Dr. Tsing tells him that a blood exchange might save him, but it can be risky. Jasper does it anyways in order to save Maya. During the procedure, Monty starts to ask questions to Tsing. Though she tries to get Monty to leave the room, he stays after he catches her in the middle of a lie. After the procedure is a success and Maya is fully recovered, Tsing visits Dante Wallace and informs him that their first Human Trial was a success, however this displeases him as he stated to her he did not want any tests done.
In Fog of War, she is seen alongside Cage arguing with Dante as to extracting blood from the delinquents. Dante says he will not take them forcefully, much to their displeasure. Later she is seen alongside Cage performing tests on the delinquents who volunteered to give blood to the Mountain Men.
In Long Into an Abyss, Tsing and Cage perform a test on Keenan Mykulak in order to test the blood transfusions the delinquents gave. Keenan however starts getting radiation burns almost instantly. Cage tries to stop it, but Tsing steps in saying that she will clearly inform everyone of what they are doing, so they allow Keenan to die. They determine that a Bone Marrow is required in order to get the full effect from their blood, so they abduct Harper and perform a Bone Marrow on her.
In Coup de Grâce, she is confronted by Dante, who is performing Bone Marrow's on Harper and locked upMonty Green. He arrests her for her actions, freeing the two. Dr. Tsing says that the ground is their birth right, and they belong to be out there, but Dante disagrees and arrests her anyways.
In Rubicon, after being freed by the new president Cage, Dr. Tsing is seen entering the Delinquents room, who are now isolated in their room. She walks in telling them they need all of them to obtain their blood, and starts taking them one by one. She is seen performing a Bone Marrow on one delinquent, extracting all of his blood. Later when she is racking up the others, the delinquents start to rebel, with their plan ultimately failing. She then chooses to take Jasper to perform an operation on, with the guards dragging him out. However,Bellamy Blake causes a radiation leak, killing all the guards but Tsing attempts to escape via elevator. However, Jasper holds the door open, with Jasper, Miller, Monty and Harper watching her slowly die.
In Blood Must Have Blood (Part 1), she is mentioned by Cage when he announces to the citizens of Mount Weather that before his "friend" was murdered, she found a treatment to help them get to the ground safely.