Fire Must Burn by Allison Montclair
This installment of the Sparks & Bainbridge series harkens back to Iris's days at Cambridge. An old university friend named Tony, who like Iris worked for government intelligence, has returned to London. Iris's former spy boss wants to know if he's working for the enemy and enlists the help of Iris and Gwen and their marriage bureau. Then someone tries to kill Tony, and Iris begins to believe it's tied to an incident that happened in the past. A compelling story with our two likeable heroines.