‘The Museum‘ recruited 4 girls in the ‘70s as Project Sphinx assassins; now they‘re meeting on a cruise to celebrate their retirement. Switches (currently; ch 5) between now (in past tense in the 1st person from Billie‘s POV) and the ‘70s (in - confusingly 🙃 - present tense, 3rd person) when they were recruited & sent on their first mission.
Picked this up because I read & enjoyed Richard Osborne‘s Thursday Club & sequel