Context : This study follows up the previous analysis of lower-angular resolution data in which the kinematics and structure of the circumstellar envelope ( CSE ) around the S-type asymptotic giant branch ( AGB ) star \pi ^ { 1 } Gruis were investigated .
The AGB star has a known companion ( at a separation of \sim 400 AU ) which can not explain the strong deviations from spherical symmetry of the CSE .
Recently , hydrodynamic simulations of mass transfer in closer binary systems have successfully reproduced the spiral-shaped CSEs found around a handful of sources .
There is growing evidence for an even closer , undetected companion complicating the case of \pi ^ { 1 } Gruis further .

Aims : The improved spatial resolution allows for the investigation of the complex circumstellar morphology and the search for imprints on the CSE of the third component .

Methods : We have observed the ^ { 12 } CO J =3-2 line emission from \pi ^ { 1 } Gruis using both the compact and extended array of Atacama Large Millimeter/submillimeter Array ( ALMA ) .
The interferometric data has furthermore been combined with data from the ALMA total power ( TP ) array .
The imaged brightness distribution has been used to constrain a non-local , non-LTE 3D radiative transfer model of the CSE .

Results : The high-angular resolution ALMA data have revealed the first example of a source on the AGB where both a faster bipolar outflow and a spiral pattern along the orbital plane can be seen in the gas envelope .
The spiral can be traced in the low- to intermediate-velocity ( 13–25 km s ^ { -1 } ) equatorial torus .
The largest spiral-arm separation is \approx 5 \aas@@fstack { \prime \prime } 5 and consistent with a companion with an orbital period of \approx 330 yrs and a separation of less than 70 AU .
The kinematics of the bipolar outflow is consistent with it being created during a mass-loss eruption where the mass-loss rate from the system increased by at least a factor of 5 during 10-15 yrs .

Conclusions : The spiral pattern is the result of an undetected companion .
The bipolar outflow is the result of a rather recent mass-loss eruption event .