He therefore summoned Plautianus in haste, as if upon some other business. And Plautianus hurried so, or rather Heaven gave him such an intimation of his approaching destruction, that the mules that brought him dropped in the palace yard. 2 And when he entered, the porters at the latticed gates admitted him alone inside and would permit no one else to go in with him, just as he himself had once done in the case of Severus at Tyana. This caused him to suspect something, and he became alarmed; but as he had no way of withdrawing, he went in. 3 Severus talked to him in a very mild manner, and asked: "Why have you seen fit to do this? Why did you wish to kill us?" He also gave him an opportunity to speak and acted as if intending to listen to his defence. But Antoninus, as Plautianus was making denial and expressing amazement at what was said, rushed up, took away his sword, and p247 struck him with his fist; 4 and he even wanted to kill him with his own hands, after the other had remarked, "You have forestalled me in killing." But, being prevented by his father, Antoninus ordered one of the attendants to slay Plautianus.
This seems a little suspicious to me. it seems that Severus was more than willing to believe that Plautianus had plotted against him and was prepared to get rid of him. t doesn't seem like Severus cared as much for him as Cassius' writings had said previously.