The invention relates to a thrust reverser for a turbofan engine nacelle including a stationary portion (15) downstream from which is mounted at least one cowl (9) movable between a direct-jet position, in which the cowl (9) is aligned with the stationary portion (15), and a thrust-reversal position, in which the mobile cowl (9) is spaced apart from the stationary portion (15) so as to define an opening for the passage of a secondary flow (F), a means for deflecting (16) the secondary flow (F) through the passage opening, an actuator means (45) and a means (24) for guiding the mobile cowl (9) relative to the stationary portion (15), at least a first and a second adjacent cascade vane (13), positioned at an angle (B) relative to the movement axis (A) of the mobile cowl (9), arranged opposite the passage opening such that the deflected secondary flow (F) at least partially passes through the first and second vanes (13) in order to increase the deflection of said secondary flow (F) in the upstream direction, said actuator means (45) and means (24) for guiding the mobile cowl (9) being arranged between the first and second vanes (13). A covering wall (31) connects said first and second vanes (13), bypassing said actuator means (45) and guiding means (24).