Complex sentence: After the Tenth Doctor says goodbye, the Fifth Doctor reminds him to raise the TARDIS' shields, but it is too late, seconds after, the "Titanic" collides with the TARDIS, leading the narrative into "Voyage of the Damned".
Split into simpler sentences: After the Tenth Doctor says goodbye, the Fifth Doctor reminds him to raise the TARDIS' shields. Seconds after, the "Titanic" collides with the TARDIS, leading the narrative into "Voyage of the Damned".