Will Arrowsmith was a junior science officer of UNIT who acted as the assistant of its scientific advisor Elizabeth Klein during the early 1990s. He was on probation to become a full member of UNIT when he saw an opportunity to prove his skills in the field and decided to follow Klein and the Doctor into the TARDIS, getting involved in the search for the persuasion machine. (AUDIO: Persuasion)
Before the Doctor Edit
Will was on probation to formally join UNIT. According to Elizabeth Klein, he was very intelligent and his research papers were superb, but his work on the field was underwhelming and poor. He was involved in at least three failed missions in Bangalore, Yarmouth Pier and Mexico City. While he claimed to be trying his best, Klein and members of staff considered him to be more adept at a desk job, disillusioning Will. (AUDIO: Persuasion)
Meeting the Doctor Edit
While on an informal meeting at a pub with Klein, Will noticed the presence of the Seventh Doctor in the pub and informed Klein, fearing a new "blue box incident". Klein ordered him to inform UNIT command of the presence of the Doctor while she followed him. He asked to come with her but she refused. Deciding to prove himself to her in the field, he directly disobeyed orders and followed her into the Doctor's TARDIS. Inside, he explored for a while before realising they had landed and that both Klein and the Doctor had already exited, so he followed them outside.
Landing in Dusseldorf in May 1945, Will went out to search for the Doctor but bumped into Lucas Hinterberger instead. Hinterberger threatened to kill Will until the Doctor and Klein appeared and it seemed to calm him down. At that moment, the Klecht entity informed them that they were planning on detonating a bomb to kill them, so the Doctor gave Will his sonic screwdriver and told him to defuse the bomb. He managed to figure out how it worked, but was unable to cancel the detonation until the arrival of the Doctor. Hinterberger told them about the struwwelpeter and agreed to tell them the location of Kurt Schalk, the scientist the Doctor had come to search for in the first place.
After materialising on the Greek island of Minos where Schalk was hiding, Hinterberger became afraid and ran, with Will running after him. When he caught up to him, they both came in contact with the struwwelpeter, but the meeting left them unconscious. After recovering, they went to find the Doctor. When they came into contact again, they learned that the struwwelpeter were actually godlike beings that came from another universe and considered this universe to be corrupt. The struwwelpeter gave Schalk the information to build a device known as the persuasion machine that could manipulate everyone to follow the will of whoever possessed it. The Doctor offered to take the struwwelpeter to another planet that was more beautiful. However, this was a lie so the Doctor could trap them in the planet which he later trapped in the TARDIS's star chamber. While this happened, Schalk was taken by the Klecht entity, so the Doctor, Will and Klein pursued him to prevent the persuasion machine being used. (AUDIO: Persuasion)
The Doctor located both Schalk and the persuasion machine being auctioned by an old acquaintance of the Doctor called Garundel to several warmongering species. So as to not make Garundel suspicious, the Doctor sent Klein and Will undercover to investigate the location of Schalk and the machine, as well as to provide the Doctor an opening in Garundel's defences for the TARDIS to get through.
While investigating, Will started to like Garundel's assistant named Ziv. He followed her to discover the weapons' and Schalk's location. He infiltrated the location of the weapons, but got trapped inside it. Investigating it, he found the body of Schalk. When Ziv returned, Will gave the Doctor the signal to land, but was discovered and captured by her and taken along with her in a space ship disguised as a store room. During the escape, Will reprimanded Ziv for her lies and scheming until Garundel remotely disabled their ship. He asked her to travel with them if possible. He also learned that the man in the ship was not really Kurt Schalk.
They were caught by Garundel along with the Doctor and the Sontaran battle fleet who had captured Klein. The Doctor escaped to their ship. Will then negotiated the exchange for Klein and learned the dead man being auctioned was not really Schalk but Hinterberger. Schalk used the machine on Hinterberger and himself. Will was saddened to hear Ziv wasn't coming, made unaware that she had been killed by Garundel by Klein to spare his feelings. (AUDIO: Starlight Robbery)
They returned to Minos in 1945 and discovered the Daleks had captured Schalk. The Doctor found them in the planet Azimuth, a planet visited by the Doctor and his companion Ace, while recalling the events transpired there the Doctor mentioned the previous Dalek occupation which alerted the authorities and Will got captured. The Superintendent Qaren who was against the law that prohibited the mention of the Daleks and the occupation took him to meet with Father, there he asked Will to bring the Doctor to him. He returned to the Doctor and Klein but mentioned the Daleks and were chased again while the Doctor went to meet with Father, Klein abandoned Will and left in the TARDIS leaving him to be captured again.
Will was taken by a man named Falkus to the Dalek lair where he found Schalk was now leader of the Daleks who interrogated him. When they brought the Doctor to them Schalk was going to torture Will to make the Doctor talk, he told what happened to Klein and that she went to 1945 again to see her creation, the Doctor revealed Schalk to be the biological father of Klein and her creation as a tool for the use of the persuasion machine, at that moment Klein returned in the TARDIS and acted like a Nazi willing to be used with the machine. At that moment Falkus entered the room and ordered the extermination of Schalk, he was sent to a prison cell but was rescued by a duplicate of Qaren and taken with her and Davros to rescue Klein, he tried to reason with her, he recovered the TARDIS key and left to free the Shepard to save them but it reversed and it threatened to kill them, Klein killed it with the machine but sacrificed herself in the process. The Doctor and him realised that it wasn't really Klein but her biological mother, they then tracked her to Russia in 1945, as they were being chased by Russian soldiers the Doctor called it an adventure. (AUDIO: Daleks Among Us)
Will was a very introverted man, often acting nervous around other people and indecisive when needed to take action. He was oblivious to the effect his presence and quirks had on others and seemed to have difficulty getting along with other people.
When addressing others he was very proper and formal, always addressing Dr. Klein by her title or by ma'am and seeming to speak with utmost respect towards others.
He was very intelligent and logical, being able to comprehend situations and details regarding the lifeforms they encountered.
He was also prone to certain compulsions, such as having to record his thoughts both alone and in the presence of others for reflection and relief. He also had the tendency to speak to himself when alone. (AUDIO: Persuasion)
During his travels with the Doctor, he seemed to be able to adapt more to the situations they encountered and started to gain both skill and confidence in field work.
By his own claims, he seemed to not be very good regarding romantic affairs, though he was capable of speaking to girls he found attractive, even flirting with and inviting the alien Ziv to travel with them. (AUDIO: Starlight Robbery)