The "Dead Letter" is Y as the unit tries to grapple with the latest twist in bomb disarmment. Brian gets posted to Cambridge to work with Dr. Gillespie and his assistant on a way to defuse this one, which leads to an uncomfortable reunion with Susan (not sure which would be worse, a bomb exploding or a broken heart revisited). They decide the best way to deal with the bomb is to use liquid oxygen to freeze the battery in the fuse, rendering it harmless (yea, -22 degrees Centigrade should do it). The process is long but it works. The episode ends with a twist of fate for Brian and Susan.
Please read the following before uploading
Do not upload anything which you do not own or are fully licensed to upload. The images should not contain any sexually explicit content, race hatred material or other offensive symbols or images. Remember: Abuse of the TV.com image system may result in you being banned from uploading images or from the entire site – so, play nice and respect the rules!