### Clue: Trinity Hall, reading electrical engineering, student starts delving into book (9)
### Answer: THREESOME 
 ### Explanation: Trinity Hall, reading electrical engineering, student starts delving into book (9)
**H**(all) **R**(eading) **E**(lectrical) **E**(ngineering) **S**(tudent) [*starts*] *delving into* **TOME** ("book")