Context : The O6 Vn star HD 64315 is believed to belong to the star-forming region known as NGC 2467 , but previous distance estimates do not support this association .
Moreover , it has been identified as a spectroscopic binary , but existing data support contradictory values for its orbital period .

Aims : We explore the multiple nature of this star with the aim of determining its distance , and understanding its connection to NGC 2467 .

Methods : A total of 52 high-resolution spectra have been gathered over a decade .
We use their analysis , in combination with the photometric data from All Sky Automated Survey and Hipparcos catalogues , to conclude that HD 64315 is composed of at least two spectroscopic binaries , one of which is an eclipsing binary .
We have developed our own program to fit four components to the combined line shapes .
Once the four radial velocities were derived , we obtained a model to fit the radial-velocity curves using the Spectroscopic Binary Orbit Program ( SBOP ) .
We then implemented the radial velocities of the eclipsing binary and the light curves in the Wilson-Devinney code iteratively to derive stellar parameters for its components .
We were also able to analyse the non-eclipsing binary , and to derive minimum masses for its components which dominate the system flux .

Results : HD 64315 contains two binary systems , one of which is an eclipsing binary .
The two binaries are separated by \sim 0.09 \ > arcsec ( or \sim 500 \ > AU ) if the most likely distance to the system , \sim 5 \ > kpc , is considered .
The presence of fainter companions is not excluded by current observations .
The non-eclipsing binary ( HD 64315 AaAb ) has a period of 2.70962901 \pm 0.00000021 \ > d. Its components are hotter than those of the eclipsing binary , and dominate the appearance of the system .
The eclipsing binary ( HD 64315 BaBb ) has a shorter period of 1.0189569 \pm 0.0000008 \ > d. We derive masses of 14.6 \pm 2.3 \ > M _ { \odot } for both components of the BaBb system .
They are almost identical ; both stars are overfilling their respective Roche lobes , and share a common envelope in an overcontact configuration .
The non-eclipsing binary is a detached system composed of two stars with spectral types around O6 V with minimum masses of 10.8 \ > M _ { \odot } and 10.2 \ > M _ { \odot } , and likely masses \approx 30 \ > M _ { \odot } .

Conclusions : HD 64315 provides a cautionary tale about high-mass star isolation and multiplicity .
Its total mass is likely above 90 \ > M _ { \odot } , but it seems to have formed without an accompanying cluster .
It contains one the most massive overcontact binaries known , a likely merger progenitor in a very wide multiple system .