  On 15 May 2005, a huge interplanetary coronal mass ejection (ICME) was
observed near Earth. It triggered one of the most intense geomagnetic storms of
solar cycle 23 (Dst peak = -263 nT). This structure has been associated with
the two-ribbon flare, filament eruption, and coronal mass ejection originating
in active region 10759 (NOAA number). We analyze here the sequence of events,
from solar wind measurements (at 1 AU) and back to the Sun, to understand the
origin and evolution of this geoeffective ICME. From a detailed observational
study of in situ magnetic field observations and plasma parameters in the
interplanetary (IP) medium and the use of appropriate models we propose an
alternative interpretation of the IP observations, different to those discussed
in previous studies. In our view, the IP structure is formed by two extremely
close consecutive magnetic clouds (MCs) that preserve their identity during
their propagation through the interplanetary medium. Consequently, we identify
two solar events in H{\alpha} and EUV which occurred in the source region of
the MCs. The timing between solar and IP events, as well as the orientation of
the MC axes and their associated solar arcades are in good agreement.
Additionally, interplanetary radio type II observations allow the tracking of
the multiple structures through inner heliosphere and pin down the interaction
region to be located midway between the Sun and the Earth. The chain of
observations from the photosphere to interplanetary space is in agreement with
this scenario. Our analysis allows the detection of the solar sources of the
transients and explains the extremely fast changes of the solar wind due to the
transport of two attached (though nonmerging) MCs which affect the
magnetosphere.
