Complex sentence: Although Singh did not witness the assault, he vowed to take revenge, and joined other revolutionaries, Shivaram Rajguru, Sukhdev Thapar and Chandrashekhar Azad, in a plot to kill Scott.
Split into simpler sentences: Although Singh did not witness the assault, he vowed to take revenge. He conspired with Shivaram Rajguru, Sukhdev Thapar and Chandrashekhar Azad, who were also revolutionaries, in a plot to kill Scott.