Lucky Luke - Volume 49 - The Dalton's amnesia

After a fellow inmate, having received a blow to the head, forgets his own
name and is freed as a brand new man, the Daltons start pretending to be
amnesiac in order to escape the prison. So as to test their supposed amnesia –
and hopefully allow them to retrieve their memories should it be real – they
are put in familiar situations: bank hold-ups, train robberies … under Lucky
Luke’s supervision, of course.