The writing is simple, pared down. An old married man and woman, Mub (pronounced 'Meub') and Mab, are ailing and live for the postman bringing letters from their son and daughter, Tir and Lir, one from each of them arriving every Monday, and the play is set over a ten-week period: so ten letters.
Tir is in the army and the first letter in the play reveals that a stray bullet has hit his leg and that he is in hospital. Lir is obviously a prostitute (prostitution being a common theme in Redonnet's work), and although the name of her job isn't specifically mentioned her first letter reveals that she has a fever which is putting her clients off.
After each letter Mub writes back to Tir and Lir, and in spite of a brief remission of both of them things get worse. Tir has a have his leg cut off and will receive a pension, and Lir is hospitalised as she has a 'microbe'. In proportion as the health of Tir and Lir worsen, so to do the mobility and general health of Mab and Mub, and any hopes of the four joining each other in a home, any hopes even of them meeting again, are dispelled slowly.
Not that there are any surprises here: quite early in the play it becomes evident that the eventual death of all four of them is inevitable, that Mab and Mub will be the only two characters in the play, and that they and their son and daughter will die miserably. The final letters arrive as usual on Monday, only one is written by Tir's superior officer, one by Lir's doctor, to inform their parents of their son and daughter's imminent death. Time for Mab and Mub to die together in their hovel.
Strangely, this is not as slit-your-throat depressing as it reads, and it's almost as if Beckett had been reborn (even though he was still (just) alive at time of publication of Tir & Lir).
Links to my other Marie Redonnet posts:
Marie Redonnet: Rose Mélie Rose | Mellie Rose
Marie Redonnet: Seaside
Marie Redonnet: Nevermore